drm/amdgpu: drop unused structures in amdgpu_drm.h

These were never used and are duplicated with the
interface that is used.  Maybe leftovers from a previous
revision of the patch that added them.

Fixes: 90c448fe ("drm/amdgpu: add new AMDGPU_INFO subquery for userq objects")
Reviewed-by: Prike Liang <Prike.Liang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>