drm/msm: Remove exclusive-fence hack

The workaround was initially necessary due to dma_resv having only a
single exclusive fence slot, yet whe don't necessarily know what order
the gpu scheduler will schedule jobs.  Unfortunately this workaround
also has the result of forcing implicit sync, even when userspace does
not want it.

However, since commit 047a1b87 ("dma-buf & drm/amdgpu: remove
dma_resv workaround") the workaround is no longer needed.  So remove
it.  This effectively reverts commit f1b3f696

 ("drm/msm: Don't
break exclusive fence ordering")

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/509457/
Link: https://lore.kernel.org/r/20221101214051.159988-1-robdclark@gmail.com