proc: remove proc_tty_ldisc variable

/proc/tty/ldisc appear to be unused as a directory and
it had been always that way.

But it is userspace visible thing.

Cowardly remove only in-kernel variable holding it.

[akpm@linux-foundation.org: add comment]
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/proc_tty.c

@@ -18,7 +18,7 @@
 /*
  * The /proc/tty directory inodes...
  */
-static struct proc_dir_entry *proc_tty_ldisc, *proc_tty_driver;
+static struct proc_dir_entry *proc_tty_driver;
 
 /*
  * This is the handler for /proc/tty/drivers
@@ -176,7 +176,7 @@ void __init proc_tty_init(void)
 {
 	if (!proc_mkdir("tty", NULL))
 		return;
-	proc_tty_ldisc = proc_mkdir("tty/ldisc", NULL);
+	proc_mkdir("tty/ldisc", NULL);	/* Preserved: it's userspace visible */
 	/*
 	 * /proc/tty/driver/serial reveals the exact character counts for
 	 * serial links which is just too easy to abuse for inferring