autofs4_kill_sb() doesn't need to be declared as extern, and no other
functions in .h are explicitly declared as extern.

Link: http://lkml.kernel.org/r/20160812024739.12352.99354.stgit@pluto.themaw.netSigned-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.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>