drm/nouveau/kms/nv50-: remove unused functions

stable inclusion
from stable-v5.10.175
commit 9ca74e5e75ea29399cbec3102bb195a1d899fa4a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8711T

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ca74e5e75ea29399cbec3102bb195a1d899fa4a



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[ Upstream commit 89ed996b ]

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Stable-dep-of: 3638a820 ("drm/nouveau/kms/nv50: fix nv50_wndw_new_ prototype")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>