Bump debhelper from old 12 to 13.

+ debian/rules: Drop --fail-missing argument to dh_missing, which is now the default.

Changes-By: lintian-brush
Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html