drm/nouveau: Remove waitque for sched teardown

drm/nouveau: Remove waitque for sched teardown

struct nouveau_sched contains a waitque needed to prevent
drm_sched_fini() from being called while there are still jobs pending.
Doing so so far would have caused memory leaks.

With the new memleak-free mode of operation switched on in
drm_sched_fini() by providing the callback nouveau_sched_cancel_job()
the waitque is not necessary anymore.

Remove the waitque.

Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://lore.kernel.org/r/20250710125412.128476-10-phasta@kernel.org