autofs: remove wrong comment

This format seems to have been taken from device mapper header, but
autofs has no such file:function in both kernel and userspace.

Link: http://lkml.kernel.org/r/148577164094.9801.4775075118014742496.stgit@pluto.themaw.net


Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>