drm/nouveau: Remove the unused header file nvif/list.h

The nouveau driver depends on include/linux/list.h instead of
nvif/list.h, so remove the obstacle-nvif/list.h.

Signed-off-by: Cai Huoqing <cai.huoqing@linux.dev>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209065322.43938-1-cai.huoqing@linux.dev