drm: Drop connector argument from __drm_atomic_helper_connector_destroy_state

It's unused, and really this helper should only look at the state
structure and nothing else. Note that this conflicts with a patch from
Dave that adds refcounting to drm_connectors. It's not yet clear
whether the check Dave adds for connector != NULL is really needed or
the right check.

v2: Fix commmit message (Laurent).

Cc: Dave Airlie <airlied@gmail.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462804451-15318-3-git-send-email-daniel.vetter@ffwll.ch