drm/ttm: fix removal of bo_count sysfs file

Only a zombie leftover from rebasing.

Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 3763d635 ("drm/ttm: add debugfs directory v2")
Reported-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210209131756.24650-1-christian.koenig@amd.com