Revert "Allow room moderators to view redacted event content"

This reverts commit 2dc2979af5.

The feature was merged to upstream, and merging upstream will be cleaner
without this commit here.

synapse/storage/databases/main/events_worker.py

@@ -303,15 +303,6 @@ class EventsWorkerStore(SQLBaseStore):
             desc="get_received_ts",
         )
 
-    async def have_censored_event(self, event_id: str) -> Optional[bool]:
-        return await self.db_pool.simple_select_one_onecol(
-            table="redactions",
-            keyvalues={"redacts": event_id},
-            retcol="have_censored",
-            desc="get_have_censored",
-            allow_none=True,
-        )
-
     # Inform mypy that if allow_none is False (the default) then get_event
     # always returns an EventBase.
     @overload