After commit 4279f3f988 ("staging: erofs: turn cache
strategies into mount options"), cache strategies are
changed into mount options rather than old build configs.
Let's kill useless code for obsoleted build options.
Link: https://lore.kernel.org/r/20191008125616.183715-2-gaoxiang25@huawei.com
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>