Fix bad with start_background_tasks

This was originally removed in #18886
but it looks like it snuck back in #18828
during a bad merge

Author: MadLittleMods

synapse/server.py

@@ -613,12 +613,6 @@ def setup(self) -> None:
         self.datastores = Databases(self.DATASTORE_CLASS, self)
         logger.info("Finished setting up.")
 
-        # Register background tasks required by this server. This must be done
-        # somewhat manually due to the background tasks not being registered
-        # unless handlers are instantiated.
-        if self.config.worker.run_background_tasks:
-            self.start_background_tasks()
-
     # def __del__(self) -> None:
     #    """
     #    Called when an the homeserver is garbage collected.