get rid of s_files and files_lock

The only thing we need it for is alt-sysrq-r (emergency remount r/o)
and these days we can do just as well without going through the
list of files.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
static int compare_single(struct super_block *s, void *p)
{
	return 1;
}

static int compare_single(struct super_block *s, void *p)
{
	return 1;
}
