remove mentionings of devfs in documentation

Now that devfs is removed, there's no longer any need to document how to
do this or that with devfs.

This patch includes some improvements by Joe Perches.

Signed-off-by: Adrian Bunk <bunk@stusta.de>

Documentation/filesystems/tmpfs.txt

@@ -39,7 +39,7 @@ tmpfs has the following uses:
 	tmpfs	/dev/shm	tmpfs	defaults	0 0
 
    Remember to create the directory that you intend to mount tmpfs on
-   if necessary (/dev/shm is automagically created if you use devfs).
+   if necessary.
 
    This mount is _not_ needed for SYSV shared memory. The internal
    mount is used for that. (In the 2.3 kernel versions it was