drm/atomic: Remove inexistent reference

Commit 63e83c1d ("drm: Consolidate connector arrays in
drm_atomic_state") removed the connector_states field but didn't remove
its mention in the num_connectors documentation.

Acked-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20231214100917.277842-2-mripard@kernel.org


Signed-off-by: Maxime Ripard <mripard@kernel.org>