Remove legacy code of single user device resync api

changelog.d/15418.removal

@@ -0,0 +1 @@
+Since multi-user device resync api is now available, single user counterpart is removed.

synapse/handlers/device.py

@@ -14,7 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from http import HTTPStatus
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -919,12 +918,8 @@ class DeviceListWorkerUpdater:
     def __init__(self, hs: "HomeServer"):
         from synapse.replication.http.devices import (
             ReplicationMultiUserDevicesResyncRestServlet,
-            ReplicationUserDevicesResyncRestServlet,
         )
 
-        self._user_device_resync_client = (
-            ReplicationUserDevicesResyncRestServlet.make_client(hs)
-        )
         self._multi_user_device_resync_client = (
             ReplicationMultiUserDevicesResyncRestServlet.make_client(hs)
         )
@@ -948,17 +943,8 @@ async def multi_user_device_resync(
 
         try:
             return await self._multi_user_device_resync_client(user_ids=user_ids)
-        except SynapseError as err:
-            if not (
-                err.code == HTTPStatus.NOT_FOUND and err.errcode == Codes.UNRECOGNIZED
-            ):
-                raise
-
-            # Fall back to single requests
-            result: Dict[str, Optional[JsonDict]] = {}
-            for user_id in user_ids:
-                result[user_id] = await self._user_device_resync_client(user_id=user_id)
-            return result
+        except:
+            raise
 
     async def user_device_resync(
         self, user_id: str, mark_failed_as_stale: bool = True