drm/amdgpu: remove superflous UVD encode entity

Not sure what that was every used for, but now it is completely unused.

Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>