Drop Workbench Moderation support

Attaching my WIP patch.

Note that Moderation dashboard scheduled updates depends on Scheduled Updates module which currently not supports Content moderation: #2821916: Scheduled Updates does not work with Content Moderation

Here's a re-roll of #2 - I also removed the moderation_dashboard_scheduled_updates sub-module since we won't be able to get it working (well) without #2821916: Scheduled Updates does not work with Content Moderation being committed. We can add it back later, but shouldn't include it in a release if it depends on a patch.

Found a tiny bug - This is ready for review and RTBC now if either of you have time.

Let's remove the note sub-module as well - Moderation Note has changed since then and now has a superior tab for viewing assigned notes.

+++ b/tests/src/Kernel/ModerationDashboardTest.php
@@ -2,9 +2,8 @@
+use Drupal\Tests\content_moderation\Traits\ContentModerationTestTrait;

I (still) think that this test is a functional test and not a Kernel test, so namespace should be Drupal\Tests\moderation_dashboard\Functional;

Nothing else :)

Looks good to me, thanks for all the work!