Camera: Reuse the ScreenNail's SurfaceTexture

The Camera Util class uses an unsynced mSurfaceTexture object. Remove this reference and
use the ScreenNail's one.
JIRA: CYAN-2079
Issue: https://jira.cyanogenmod.org/browse/CYAN-2079

Change-Id: I3143ce3288fbf9439fa3c6c06de34e672d415d78
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>