Drupal - How do I remove the "submitted by" text on node display?

You can find the option by editing the content type settings.

Structure > Content Types > Type Name

Click Edit

Then uncheck the Display author and date information. option in Display Settings.

For the "basic page" type, it would be example.com/admin/structure/types/manage/page/edit. For the "article" type, it's example.com/admin/structure/types/manage/article/edit.

Module Submitted By is a more fine-grained solution FWIW. Here is a quote about it (from the module's project page):

... lets you control the format of the "Submitted by" information on your content per content type. It adds a fieldset to your node edit form called Appearance that lets you put in a tokenized pattern for the text you want to display.

Depends on Token module. Note: This module does not create any data; rather it relies on other modules providing that data through Token.

You might find the Custom Tokens module useful for things that aren't already provided.