With earlier commit 9c84aeba ("drm/vmwgfx: Kill unneeded legacy
security features") we removed the no longer applicable validation, as
we now have isolation of primary clients from different master realms.

As of last commit, we're explicitly checking for authentication in the
only render ioctls which care about one.

With those in place, the DRM_AUTH token serves no real purpose. Let's
drop it.

Cc: VMware Graphics <linux-graphics-maintainer@vmware.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>