I hate it when distros (*cough*Ubuntu*cough*) remove packages between major releases. It seems like I run into this every time! The latest, which I encountered today, is mediawiki is no longer packaged in Ubuntu 16.04 LTS but it was in 14.04 LTS. Super annoying.
At least in Gentoo removed packages get a news item and/or a post_install message that says something like "hey, this is going away in xx days. you might want to figure shit out before that"