drm/msm/gem: Remove active refcnt

At this point the pinned refcnt is sufficient, and the shrinker is
already prepared to encounter objects which are still active according
to fences attached to the resv.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/496122/
Link: https://lore.kernel.org/r/20220802155152.1727594-9-robdclark@gmail.com