kill bogus BUG_ON() in do_close_on_exec()

It can be legitimately triggered via procfs access.  Now, at least
2 of 3 of get_files_struct() callers in procfs are useless, but
when and if we get rid of those we can always add WARN_ON() here.
BUG_ON() at that spot is simply wrong.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/file.c

@@ -685,7 +685,6 @@ void do_close_on_exec(struct files_struct *files)
 	struct fdtable *fdt;
 
 	/* exec unshares first */
-	BUG_ON(atomic_read(&files->count) != 1);
 	spin_lock(&files->file_lock);
 	for (i = 0; ; i++) {
 		unsigned long set;