msm: mdss: Remove deprecated vsync pending variable

vsync pending variable is deprecated and hence remove its
usage from all places in MDSS. Reenabling vsync ctrl once
panel is on now relies on user space application.

CRs-Fixed: 513502
Change-Id: I4b3062012983c1de98a5e59b4368e028eb6b46a5
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>