vfs: remove unused superblock helpers

Remove the 'sb_mark_dirty()', 'sb_mark_clean()' and 'sb_is_dirty()'
helpers which are not used. I introduced them 2 years and the
intention was to make all file-systems use them in order to be able to
optimize 'sync_supers()'.  However, Al Viro vetoed my patches at the
end and asked me to push superblock management down to file-systems
and get rid of the 's_dirt' flag completely, as well as kill
'sync_supers()' altogether. Thus, remove the helpers.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

include/linux/fs.h

@@ -1870,19 +1870,6 @@ extern struct dentry *mount_pseudo(struct file_system_type *, char *,
 	const struct dentry_operations *dops,
 	unsigned long);
 
-static inline void sb_mark_dirty(struct super_block *sb)
-{
-	sb->s_dirt = 1;
-}
-static inline void sb_mark_clean(struct super_block *sb)
-{
-	sb->s_dirt = 0;
-}
-static inline int sb_is_dirty(struct super_block *sb)
-{
-	return sb->s_dirt;
-}
-
 /* Alas, no aliases. Too much hassle with bringing module.h everywhere */
 #define fops_get(fops) \
 	(((fops) && try_module_get((fops)->owner) ? (fops) : NULL))