Remove the obsolete MSC1849 configuration flag. (#11843)

MSC1849 was replaced by MSC2675, which was merged.
The configuration flag, which defaulted to true, is no
longer useful.

changelog.d/11843.removal

+Remove the `experimental_msc1849_support_enabled` flag as the features are now stable.

synapse/config/experimental.py

@@ -24,8 +24,6 @@ class ExperimentalConfig(Config):
     def read_config(self, config: JsonDict, **kwargs):
         experimental = config.get("experimental_features") or {}
 
-        # Whether to enable experimental MSC1849 (aka relations) support
-        self.msc1849_enabled = config.get("experimental_msc1849_support_enabled", True)
         # MSC3440 (thread relation)
         self.msc3440_enabled: bool = experimental.get("msc3440_enabled", False)
 

synapse/storage/databases/main/relations.py

@@ -75,7 +75,6 @@ class RelationsWorkerStore(SQLBaseStore):
     ):
         super().__init__(database, db_conn, hs)
 
-        self._msc1849_enabled = hs.config.experimental.msc1849_enabled
         self._msc3440_enabled = hs.config.experimental.msc3440_enabled
 
     @cached(tree=True)
@@ -683,9 +682,6 @@ class RelationsWorkerStore(SQLBaseStore):
             A map of event ID to the bundled aggregation for the event. Not all
             events may have bundled aggregations in the results.
         """
-        # If bundled aggregations are disabled, nothing to do.
-        if not self._msc1849_enabled:
-            return {}
 
         # TODO Parallelize.
         results = {}