Recycle original screenshot after rotation.

After copying the Bitmap to a new Bitmap, there is no need to keep
the original pixels.

This may help memory pressure when running automated tests and taking
lots of screenshots, although it does not fix the main source of the
problem.

BUG:15454296
Change-Id: I7e61886fbb46a8068db3e8dfa1fcb0afd88ea430