MDAD keeps `/_synapse/client/*` out of the broad worker-routing model.
Those paths are mounted by current Synapse on client-serving workers, but MDAD's
worker route buckets only match `/_matrix/client/*`, so `/_synapse/client/*`
requests already fall through to the main-process default.

That made the `/_synapse/client/*` branches in the dedicated SSO override regex
redundant. Remove those branches and leave the explicit SSO override focused on
the real `/_matrix/client/.../login/sso/redirect` path family, which would
otherwise be caught by the broad `/login` client-reader routing.

This also removes duplicated ownership of `login/sso/redirect` from the generic
main-override regex so the dedicated SSO override is the single place that
models that path.

Refs:
- b99a58719b/synapse/app/generic_worker.py (L197-L203)
- b99a58719b/synapse/rest/synapse/client/__init__.py (L39-L90)
- b99a58719b/synapse/rest/client/login.py (L636-L643)