You can always manually delete a plugin from the /plugins directory or,
if you want, you can use the php artisan vanguard:remove-plugin Foo command
and let the system delete it for you and take care of updating the main
composer.json file.
If you have installed the plugin via Composer and you want to remove it, the procedure is as easy as above. For example, if you want to remove the Vanguard official Announcements plugin that comes with Vanguard out of the box, you'll need to do the following two things:
1) Remove the \Vanguard\Announcements\Announcements::class, line from the array of active plugins in VanguardServiceProvider. This will make the plugin
inactive and it won't appear inside the Vanguard at all.
2) Run composer remove vanguardapp/announcements to completely remove the plugin
from the system.