SurfaceComposerClient: Remove mForceSynchronous flag

Legacy code forced the transaction to be sync when setting
display projection.  This shouldn't be needed as we should
be synchronizing at a higher level.

This display projection is set as part of the WM global transaction
so avoid an unnecessary sync is advantageous here.

Test: go/wm-smoke
Bug: 238781169
Change-Id: I83a213a04b3c664b0bffef4c7597d99f901a492e