Revert "cameraservice: Resolve message vs start/stop preview races"

 * This is added because we have another commit to fix some
   old issues back in KK days (see commit
   'camera: Re-add micromanagement of preview metadata'), but
   we never enable or disable metadata messages since long ago
   here, so the race is no more.

This reverts commit d29b086f.

Change-Id: I393bf8d809577b65ab881db06810e52afbbc0710