drm: Remove 2 unused defines

These were introduced in the very first DRM commit:

  commit f453ba04
  Author: Dave Airlie <airlied@redhat.com>
  Date:   Fri Nov 7 14:05:41 2008 -0800

      DRM: add mode setting support

      Add mode setting support to the DRM layer.

But are unused.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>