drm/ttm: drop ttm_bo_move_ttm wrapper

The apis to move old/new are in place everywhere so this is no
longer needed.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201019071314.1671485-6-airlied@gmail.com