camera: Always enable preview metadata

 * Remove the ifdefs which enable/disable the preview metadata during
   start/stop preview.  This causes issues with face detection and
   other uses on new hardware.
 * I am not aware of any hardware which still needs this.

Change-Id: I3dd0941a61affb4862a2e8f4f0c2cf59c95b150e
Merge remote-tracking branch 'cm/cm-11.0' into kitkat