drm/ttm: remove ttm_bo_(un)lock_delayed_workqueue

Those functions never worked correctly since it is still perfectly
possible that a buffer object is released and the background worker
restarted even after calling them.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221125102137.1801-2-christian.koenig@amd.com