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>
SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
{
	return do_sys_ftruncate(fd, length, 1);
}

SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
{
	return do_sys_ftruncate(fd, length, 1);
}
