How can I uninstall an apache2 module?

It's so simple nobody has written it down yet. You just remove the .so file from /usr/lib/apache2/modules/.

And if you want to be thorough, remove anything that might be in: /usr/share/doc/module-name

For some modules on Ubuntu you can use apt-get.

To find the installed module sudo dpkg -l | grep apache. To remove sudo apt-get purge {module_name}.

For example:

sudo apt-get purge libapache2-mod-php7.0  libapache2-mod-php5