autofs: remove obsolete sb fields

These two were left from commit aa55ddf3 ("autofs4: remove unused
ioctls") which removed unused ioctls.

Link: http://lkml.kernel.org/r/20160812024810.12352.96377.stgit@pluto.themaw.net


Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Ian Kent <ikent@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>