drm/nouveau: Do not set struct drm_mode_config_funcs.output_poll_changed

drm/nouveau: Do not set struct drm_mode_config_funcs.output_poll_changed

The output_poll_changed hook was only necessary before in-kernel
DRM clients existed, but is now obsolete. The client code handles
display hotplugging internally.

v2:
- fix commit description

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240812083000.337744-5-tzimmermann@suse.de