drm/ttm: clean up ttm_trace_dma_map/ttm_trace_dma_unmap (v2)

ttm_trace_dma_map/ttm_trace_dma_unmap is never used anymore.

v2: remove the file completely

Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/360432/