Plex mark devices unavailable if they 'vanish' and clear media (#12811)

* Marks Devices unavailable if they 'vanish' and clears media

* Fixed PEP8 complaint

* Fixed Linting

* Lint Fix

* Fix redine of id

* More lint fixes

* Removed redundant loop for setting availability of client
Renamed '_is_device_available' to '_available'
Renamed 'available_ids' to 'available_client_ids'

* removed whitespace per houndCI