remove copybit hack from software opengl (libagl)

h/w acceleration is not supported through software gl + copybit anylonger,
instead, h/w opengl must be used. in the system compositor, a new h/w
composition api will be introduced to allow h/w accelerated composition with
overlays and/or 2D blocks.

Change-Id: I04949cb074ba8c4d637319ace23497c16a58d5bf