Revert "f2fs: fix to clean previous mount option when remount_fs"

Don't clear old mount option before parse new option during ->remount_fs
like other generic filesystems.

This reverts commit 26666c8a.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>