Delete border rendering code from SurfaceFlinger.

Removed code is never used and drawing borders is done instead
by Window Manager Service. Changes revert ag/16980603 and
ag/17496275.

Bug: b/227656283
Test: presubmit
Test: SurfaceFlinger_test
Change-Id: Ib5c8bf74ad6764d65536dc60cc3c458edde86b3f