erofs: fold in postsubmit_is_all_bypassed()

No need to introduce such separated helper since
cache strategy compile configs were changed into
runtime options instead in v5.4. No logic changes.

Link: https://lore.kernel.org/r/20200121064747.138987-1-gaoxiang25@huawei.com


Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>