drm/amdgpu: remove unused TRACE_SYSTEM_STRING define
drm/amdgpu: remove unused TRACE_SYSTEM_STRING define

Port of 77cb2fea1e5fc4b083dd967f231bbf6edd96150e to
amdgpu.

Reviewed-by: Christian König <c7ea837d7a46effe4232b086213468b8b31643bf@amd.com>
Signed-off-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs