drm/atomic: Delete wrong comment.

drm_atomic_state_put is called unconditionally, so TEST_ONLY is no
different from commit.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1481812185-19098-2-git-send-email-maarten.lankhorst@linux.intel.com