drm: remove outdated doc TODO for subconnector property

This is already documented under "standard connector properties".
Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20230227122522.117580-1-contact@emersion.fr

drivers/gpu/drm/drm_connector.c

@@ -1615,7 +1615,6 @@ EXPORT_SYMBOL(drm_connector_attach_dp_subconnector_property);
  *   - overscan
  *   - saturation
  *   - select subconnector
- *   - subconnector
  */
 /**
  * DOC: Analog TV Connector Properties