How to Disable the WordPress Gutenberg Editor

If you’ve recently set up Wordpress, you may have the version which includes the new Wordpress editor, Gutenberg, from the ‘Gutenberg Team’ (not Project Gutenberg, which is a group that digitizes reading material). It may have been installed as your default editor, or you may have clicked on a button to try Gutenberg; either way now it’s your default editor, and you don’t like it, so you want to uninstall or disable Gutenberg.