This patch removes exynos_drm_crtc_cancel_page_flip call
when drm is closed because at that time, events will be released
by drm_events_release function.

Changelog v1:
- remove exynos_drm_crtc_cancel_page_flip function also because
  this funtion isn't used anymore.
Signed-off-by: NInki Dae <inki.dae@samsung.com>
Reviewed-by: NAndrzej Hajda <a.hajda@samsung.com>