msm: kgsl: Remove A4XX preemption fair scheduler

Preemption was never enabled for A4XX but there is a lot of
bookkeeping done for it. Remove this feature since it is never
enabled but corresponds to non-zero amounts of code.

Change-Id: Icc0135fd25f91f9b2a32df1d9b4c2c101ac35b65
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>