This reverts commit f2dbabe786.
This change is not needed any more because we are caching the MDP pipe
contents when closing the channel. So no need to wait for postFB finish.
Change-Id: Ia6f01c33953762cb7a97e0b2b795d9afeb60d2d9
(cherry picked from commit 441f1824593bb12a97508b426b597a16b35091e6)