Finally remove autofs4 references in the filesystems documentation.

Link: http://lkml.kernel.org/r/152626709055.28589.416082809460051475.stgit@pluto.themaw.netSigned-off-by: NIan Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>