drm/vmwgfx: Remove STDU logic from generic mode_valid function

drm/vmwgfx: Remove STDU logic from generic mode_valid function

BugLink: https://bugs.launchpad.net/bugs/2074091
[ Upstream commit dde1de06bd7248fd83c4ce5cf0dbe9e4e95bbb91 ]

STDU has its own mode_valid function now so this logic can be removed from
the generic version.

Fixes: 935f795045a6 ("drm/vmwgfx: Refactor drm connector probing for display modes")
Signed-off-by: Ian Forbes <ian.forbes@broadcom.com>
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240521184720.767-4-ian.forbes@broadcom.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>