Remove remaining bits of groups code. (#12936)

* Update worker docs to remove group endpoints.
* Removes an unused parameter to `ApplicationService`.
* Break dependency between media repo and groups.
* Avoid copying `m.room.related_groups` state events during room upgrades.

tests/rest/client/test_account.py

@@ -548,7 +548,6 @@ class WhoamiTestCase(unittest.HomeserverTestCase):
 
         appservice = ApplicationService(
             as_token,
-            self.hs.config.server.server_name,
             id="1234",
             namespaces={"users": [{"regex": user_id, "exclusive": True}]},
             sender=user_id,