Remove the "Switch Editor" button in Site Settings for some sites

[maxme]

Calypso has deprecated the classic editor and removed any way to switch to the classic editor. We're about to switch our users to the block editor as well, but we kept the option for users to switch back to the classic editor as the default.

We want to remove that "Switch Editor" option in the "Site Settings" for most sites except for a few cases:

• Self hosted sites (all of them). They can install plugins and we don't have any way to know about them.
• Jetpack sites with plugins that allows to disable Gutenberg (plugin should be installed/active):
  • https://wordpress.org/plugins/classic-editor/
  • https://wordpress.org/plugins/disable-gutenberg/
• VIP sites. In some cases, they might not use Gutenberg as default.

There might be some other exception and the first task before implementing the fix for that ticket is to list all the cases.

Equivalent ticket on WordPress for iOS: wordpress-mobile/WordPress-iOS#14864

Progress by site type:

• Simple WP.com sites
• Atomic WP.com sites