Current Synapse no longer exposes device management under
`/_matrix/client/.../account/devices`. The live client API shape is
`/devices`, `/devices/{device_id}`, and `/delete_devices`, and
MDAD already routes those real device-list-sensitive endpoints through
explicit device-list handling.

Keeping `account/devices` in the old client-reader regex therefore only
preserves stale route-model residue. While touching the same area,
refresh the `/_synapse/client/*` comment to reflect current Synapse:
client-serving generic workers now mount a meaningful Synapse-specific
client tree there, but MDAD still intentionally keeps those paths out of
its broad worker regexes because they are deployment-sensitive and
auth-sensitive.

Refs:
- b99a58719b/docs/workers.md (historical-apps)
- b99a58719b/synapse/rest/client/devices.py (L49-L150)
- b99a58719b/synapse/rest/synapse/client/__init__.py (L39-L88)