https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=967906#10 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=967906#32 seem to indicate one doesn't need both packages.
I'm guessing that all Debian systems that have been around for 10 years will probably have both packages installed. But the newest Debian systems won't. Can I safely remove resolvconf?