fs/sysv: stop using write_super and s_dirt

It does not look like sysv FS needs 'write_super()' at all, because all it
does is a timestamp update. I cannot test this patch, because this
file-system is so old and probably has not been used by anyone for years,
so there are no tools to create it in Linux. But from the code I see that
marking the superblock as dirty is basically marking the superblock buffers as
drity and then setting the s_dirt flag. And when 'write_super()' is executed to
handle the s_dirt flag, we just update the timestamp and again mark the
superblock buffer as dirty. Seems pointless.

It looks like we can update the timestamp more opprtunistically - on unmount
or remount of sync, and nothing should change.

Thus, this patch removes 'sysv_write_super()' and 's_dirt'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/sysv/sysv.h

@@ -117,7 +117,6 @@ static inline void dirty_sb(struct super_block *sb)
 	mark_buffer_dirty(sbi->s_bh1);
 	if (sbi->s_bh1 != sbi->s_bh2)
 		mark_buffer_dirty(sbi->s_bh2);
-	sb->s_dirt = 1;
 }