Wordpress - How to remove admin menu pages inserted by plugins?

You need to use the right hooks (which are not always the same as the URLs/slugs), and it doesn't hurt to use a hook that runs later (e.g., admin_init):

add_action( 'admin_init', 'wpse_136058_remove_menu_pages' );

function wpse_136058_remove_menu_pages() {

    remove_menu_page( 'edit.php?post_type=acf' );
    remove_menu_page( 'wpcf7' );
}

You can use the following to debug:

add_action( 'admin_init', 'wpse_136058_debug_admin_menu' );

function wpse_136058_debug_admin_menu() {

    echo '<pre>' . print_r( $GLOBALS[ 'menu' ], TRUE) . '</pre>';
}

This gives (for my setup) the following for the Contact Form 7 plugin menu page:

[27] => Array
        (
            [0] => Formular
            [1] => wpcf7_read_contact_forms
            [2] => wpcf7
            [3] => Contact Form 7
            [4] => menu-top menu-icon-generic toplevel_page_wpcf7 menu-top-last
            [5] => toplevel_page_wpcf7
            [6] => none
        )

The array element with key 2 is what you are looking for: wpcf7.

You probably need to set the add_action priority to a higher number and target those two new links specifically like so:

add_action( 'admin_menu', 'my_remove_menu_pages', 999 );

function my_remove_menu_pages() {
  remove_menu_page( 'edit.php' );                   //Posts
  remove_menu_page( 'upload.php' );                 //Media
  remove_menu_page( 'edit-comments.php' );          //Comments
  remove_menu_page( 'themes.php' );                 //Appearance
  remove_menu_page( 'users.php' );                  //Users
  remove_menu_page( 'tools.php' );                  //Tools
  remove_menu_page( 'options-general.php' );        //Settings
  remove_menu_page( 'edit.php?post_type=acf' );
  remove_menu_page( 'wpcf7' );
};

Advanced Custom Fields also provides a help document on how to do this for their menu here:

http://www.advancedcustomfields.com/resources/how-to/how-to-hide-acf-menu-from-clients/

Contact Form 7 also has it's own way of restricting the visibility of the menu:

http://contactform7.com/restricting-access-to-the-administration-panel/

    // PLUGINS THAT ADD AS DASHBOARD SUBMENU
    // IF THIS IS THE URL BELOW - THE PAGE VARIABLE IS WHAT I NEED ( SO WHATEVER COMES AFTER PAGE= )
    // http://example.com/wp-admin/index.php?page=iconize-plugin-update-notifier
    remove_submenu_page( 'index.php', 'iconize-plugin-update-notifier' );

    // OR FOR EXAMPLE WOOCOMMERCE DASHBOARD SUBMENU
    remove_submenu_page( 'index.php', 'wc-about' ); //WOO
    remove_submenu_page( 'index.php', 'wc-credits' ); //WOO
    remove_submenu_page( 'index.php', 'wc-translators' ); //WOO

    // CUSTOM POST TYPE TOP LEVELS
    remove_menu_page( 'edit.php?post_type={$POST_TYPE}' ); //LOOK FOR WHAT COMES AFTER POST TYPE IN THE URL
    remove_menu_page( 'edit.php?post_type=testimonials-widget' ); //TESTIMONIALS WIDGET
    remove_menu_page( 'edit.php?post_type=product' ); //WOOCOMMERCE

    // CUSTOM POST TYPE SUBMENU
     remove_submenu_page( 'edit.php?post_type={$POST_TYPE}', '{$SUBMENU_URL_VARIABLE}' ); //EXAMPLE FORMAT
     // SO IF BELOW IS THE URL
     // http://example.com/wp-admin/edit.php?post_type=testimonials-widget&page=testimonialswidget_settings
     // YOU NEED TO SEE WHATS AFTER PAGE
     remove_submenu_page( 'edit.php?post_type=testimonials-widget', 'testimonialswidget_settings' ); //TESTIMONIALS WIDGET

    // OTHER EXAMPLES
    remove_menu_page( 'revslider' ); // REVSLIDER
    remove_menu_page( 'woocommerce' ); // WOOCOMMERCE
    remove_menu_page( 'order-post-types-shop_order' ); // WOOCOMMERCE
    remove_menu_page( 'order-post-types-shop_coupons' ); // WOOCOMMERCE
    remove_menu_page( 'shortcodes-ultimate' ); // SHORTCODES ULTIMATE
    remove_menu_page( 'wp-admin-microblog/wp-admin-microblog.php' ); // ADMIN MICROBLOG
    remove_menu_page( 'snippets' ); //CODE SNIPPETS
    remove_menu_page( 'gf_edit_forms' ); // GRAVITY FORMS
        remove_submenu_page( 'gf_edit_forms', 'gf_settings' ); // GRAVITY FORMS
        remove_submenu_page( 'gf_edit_forms', 'gf_export' ); // GRAVITY FORMS
        remove_submenu_page( 'gf_edit_forms', 'gf_update' ); // GRAVITY FORMS
        remove_submenu_page( 'gf_edit_forms', 'gf_addons' ); // GRAVITY FORMS
        remove_submenu_page( 'gf_edit_forms', 'gf_help' ); // GRAVITY FORMS

        remove_submenu_page( 'cleverness-to-do-list', 'cleverness-to-do-list-settings' ); //Cleverness TODO

YOU CAN DEBUG ALL THIS WITH THE FOLLOWING TO GET ALL THE INFO YOU NEED:

if (!function_exists('debug_admin_menus')):
function debug_admin_menus() {
if ( !is_admin())
        return;
    global $submenu, $menu, $pagenow;
    if ( current_user_can('manage_options') ) { // ONLY DO THIS FOR ADMIN
        if( $pagenow == 'index.php' ) {  // PRINTS ON DASHBOARD
            echo '<pre>'; print_r( $menu ); echo '</pre>'; // TOP LEVEL MENUS
            echo '<pre>'; print_r( $submenu ); echo '</pre>'; // SUBMENUS
        }
    }
}
add_action( 'admin_notices', 'debug_admin_menus' );
endif;

The keys will give you the array values that allow you do all of this with wordpress globals (although not recommended)

function remove_submenus_all_please() {
if ( !is_admin())
        return;
  global $submenu;
    unset($submenu['index.php'][10]); // Removes Updates
  //Posts menu
 // unset($submenu['edit.php'][5]); // Leads to listing of available posts to edit
 // unset($submenu['edit.php'][10]); // Add new post
 // unset($submenu['edit.php'][15]); // Remove categories
 // unset($submenu['edit.php'][16]); // Removes Post Tags
}
add_action('admin_menu', 'remove_submenus_all_please', 999);

And to remove for certain users just do the same thing except with capabilities added:

function remove_by_caps_admin_menu() {
if ( !is_admin())
        return;
    if ( !current_user_can('manage_options') ) {
        remove_menu_page( 'revslider' ); // REVSLIDER
    } elseif ( !current_user_can('edit_posts') ) {
        remove_menu_page( 'woocommerce' ); // WOO
    } else {
    }
}
add_action('admin_menu', 'remove_by_caps_admin_menu', 999);

AND TO TIE IT ALL TOGETHER WHY NOT SHORTEN OUR CODE? YOU CAN USE ARRAYS TO AVOID WRITING remove_submenu_page 50 times. This also works with the toolbar nodes:

if ( !function_exists( 'remove_admin_menupages_in_array' ) ) {
function remove_admin_menupages_in_array() {
    if ( !is_admin())
        return;
          $admin_menus = array(
                                'revslider',
                                'woocommerce',
                                'shortcodes-ultimate',
          );

    foreach ( $admin_menus as $menu_page ) {
        if ( !current_user_can('manage_options') ) {
            remove_menu_page( $menu_page );
        }
    } // foreach
 } // function
add_action('admin_menu', 'remove_admin_menupages_in_array', 9999);
} // exists