clean-up unneeded code

now that we removed the notion of a "inUse" buffer in surfaceflinger
a lot of code can be simplified / removed.

noteworthy, the whole concept of "unlockClient" wrt. "compositionComplete"
is also gone.

Change-Id: I210413d4c8c0998dae05c8620ebfc895d3e6233d
8 files changed