staging: erofs: remove unneeded inode_operations

Currently, EROFS uses generic iops when xattr is off,
it seems unnecessary and a lot of extra code is there.
Let's follow what other filesystems do instead.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>