drm/mtk: Drop drm_vblank_cleanup

Seems entirely cargo-culted.

Cc: CK Hu <ck.hu@mediatek.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170621082850.13224-6-daniel.vetter@ffwll.ch
Link: http://patchwork.freedesktop.org/patch/msgid/20170621082850.13224-7-daniel.vetter@ffwll.ch

drivers/gpu/drm/mediatek/mtk_drm_drv.c

@@ -266,7 +266,6 @@ static void mtk_drm_kms_deinit(struct drm_device *drm)
 {
 	drm_kms_helper_poll_fini(drm);
 
-	drm_vblank_cleanup(drm);
 	component_unbind_all(drm->dev, drm);
 	drm_mode_config_cleanup(drm);
 }