drm/sti: Drop drm_vblank_cleanup

Seems entirely cargo-culted.

Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Acked-by: NVincent Abriou <vincent.abriou@st.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170524145212.27837-31-daniel.vetter@ffwll.ch

drivers/gpu/drm/sti/sti_drv.c

@@ -237,7 +237,6 @@ static void sti_cleanup(struct drm_device *ddev)
 	}
 
 	drm_kms_helper_poll_fini(ddev);
-	drm_vblank_cleanup(ddev);
 	component_unbind_all(ddev->dev, ddev);
 	kfree(private);
 	ddev->dev_private = NULL;