Make cleaning up pushers depend on the device_id instead of the token_id (#15280)

This makes it so that we rely on the `device_id` to delete pushers on logout,
instead of relying on the `access_token_id`. This ensures we're not removing
pushers on token refresh, and prepares for a world without access token IDs
(also known as the OIDC).

This actually runs the `set_device_id_for_pushers` background update, which
was forgotten in #13831.

Note that for backwards compatibility it still deletes pushers based on the
`access_token` until the background update finishes.

synapse/handlers/device.py

@@ -503,6 +503,8 @@ class DeviceHandler(DeviceWorkerHandler):
             else:
                 raise
 
+        await self.hs.get_pusherpool().remove_pushers_by_devices(user_id, device_ids)
+
         # Delete data specific to each device. Not optimised as it is not
         # considered as part of a critical path.
         for device_id in device_ids: