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/rest/client/pusher.py

@@ -126,7 +126,6 @@ class PushersSetRestServlet(RestServlet):
         try:
             await self.pusher_pool.add_or_update_pusher(
                 user_id=user.to_string(),
-                access_token=requester.access_token_id,
                 kind=content["kind"],
                 app_id=content["app_id"],
                 app_display_name=content["app_display_name"],