drm/amdgpu: Remove unused field kgd2kfd_shared_resources.num_mec

Dead code.

Change-Id: I9575aa73b5741b80dc340f953cc773385c92b2be
Signed-off-by: Jay Cornwall <Jay.Cornwall@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>