Disable ineffective AS cache

This is specifically ineffective in our setup where we have a single
AS and thus there is no caching benefit between AS'.

Author: Fizzadar

synapse/storage/databases/main/receipts.py

@@ -433,9 +433,10 @@ def f(txn: LoggingTransaction) -> List[Dict[str, Any]]:
         }
         return results
 
-    @cached(
-        num_args=2,
-    )
+    # Beeper hack: we only have one AS, so no benefit to caching this
+    # @cached(
+    #     num_args=2,
+    # )
     async def get_linearized_receipts_for_all_rooms(
         self, to_key: int, from_key: Optional[int] = None
     ) -> Dict[str, JsonDict]: