drop libkres9 and libkres-dev packages

Debian packaging as of 3.2.1-3 is no longer shipping libkres9 or
libkres-dev (see https://bugs.debian.org/923970

).  This brings the
upstream debian-style packaging in line with the Debian packaging on
that front.

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>