drm: Nuke vblank event file cleanup code

The core code now takes care of unlinking drm_events from the file in
a generic way, so this code isn't needed any more.

For those wondering where the drm_vblank_put went to: With the new
logic events only get unlinked, but still exist. Hence any resources
(like vblank counters) don't need to be released since the event user
will still process the event normally. In this case this is the
callsites of send_vblank_event, which of course already have a
drm_vblank_put.

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453756616-28942-3-git-send-email-daniel.vetter@ffwll.ch