compositor: remove old vblank code

Bug: 13613

Since commit 7115d1b4, we can't disable second (broken) vblank waiting
code.

glXSwapBuffers() already waits for v-blank (if enabled in driver), so
any other "synthetic" waiting for v-blank can reduce performance
(de-sync) without actual benefit.

This patch removes old code to prevent waiting for vblank twice.