drm/i915: Remove connectors_active from state checking.

Connectors are updated atomically now, so the only interaction
with the encoder is through base.crtc.

If it's NULL the encoder's not part of any crtc, and if it's
not NULL then active should be equal to crtc_state->active.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>