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.
Quentin Gliech