drm/atomic: Remove drm_atomic_connectors_for_crtc.

Now that connector_mask is reliable there's no need for this
function any more.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1451908400-25147-6-git-send-email-maarten.lankhorst@linux.intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>