Make user/room stats log line less verbose.

synapse/storage/data_stores/main/stats.py

@@ -332,7 +332,7 @@ class StatsStore(StateDeltasStore):
         def _bulk_update_stats_delta_txn(txn):
             for stats_type, stats_updates in updates.items():
                 for stats_id, fields in stats_updates.items():
-                    logger.info(
+                    logger.debug(
                         "Updating %s stats for %s: %s", stats_type, stats_id, fields
                     )
                     self._update_stats_delta_txn(