Only return devices with keys from /federation/v1/user/devices/ (#8198)

There's not much point in returning all the others, and some people have a
silly number of devices.

Author: richvdh

changelog.d/8198.feature

@@ -0,0 +1 @@
+Optimise `/federation/v1/user/devices/` API by only returning devices with encryption keys.

synapse/storage/databases/main/devices.py

@@ -498,9 +498,7 @@ def _get_devices_with_keys_by_user_txn(
     ) -> Tuple[int, List[JsonDict]]:
         now_stream_id = self._device_list_id_gen.get_current_token()
 
-        devices = self._get_e2e_device_keys_txn(
-            txn, [(user_id, None)], include_all_devices=True
-        )
+        devices = self._get_e2e_device_keys_txn(txn, [(user_id, None)])
 
         if devices:
             user_devices = devices[user_id]