Revert "Disable Redis get event cache"

This reverts commit 64b476a.

Author: Fizzadar

synapse/storage/databases/main/events_worker.py

@@ -246,10 +246,8 @@ def __init__(
         ]
 
         external_sharded_cache = hs.get_external_sharded_cache()
-        # TODO: temporary explicit disable of this cache due to thrashing requests
-        # burning CPU. Possibly need to move this cache to where we get events from DB.
-        if external_sharded_cache.is_enabled() and False:
-            self._get_event_cache = RedisLruCache(  # type: ignore
+        if external_sharded_cache.is_enabled():
+            self._get_event_cache = RedisLruCache(
                 cache_name="*getEvent*",
                 max_size=hs.config.caches.event_cache_size,
                 redis_shard_cache=external_sharded_cache,