drm/i915: Remove redundant drm_connector_register_all()

drm_connector_register_all() is now automatically called by
drm_dev_register(), and so we no longer have to do so ourselves (via
intel_modeset_register() after calling drm_dev_register()). Similarly
for unregistering.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466773227-7994-8-git-send-email-chris@chris-wilson.co.uk