drm/ttm: Remove two unused function declarations

Commit cd3a8a59 ("drm/ttm: remove ttm_bo_(un)lock_delayed_workqueue")
removed the implementations but not the declarations.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230809135839.13216-1-yuehaibing@huawei.com


Signed-off-by: Christian König <christian.koenig@amd.com>