Remove spurious composer validate call to avoid hang

Presumably during Doff transitions as the hardware composer post
thread was being interrupted, there was an edge case when
a validate command could be posted without following up with
present. That could lead to create/delete layer calls between
validate and present which are not supported by some HWC
implementations.

Bug: 70178957

Test: manually verified that create layer will fail if done
 between validate and present.

Change-Id: If8db231223b23370eb4ca5ae76ced1c9d88b473d
(cherry picked from commit e3117ed7d2c99afa6488bdbbba600030e4415d64)