drm/msm: remove redundant private plane cleanup

Now that drm core knows about private planes, it cleans them up for us.
Trying to do this twice results in badness.

Signed-off-by: Rob Clark <robdclark@gmail.com>

diff --cc drivers/gpu/drm/msm/mdp/mdp4/mdp4_crtc.c
Simple merge

diff --cc drivers/gpu/drm/msm/mdp/mdp5/mdp5_crtc.c
Simple merge