Purge libllvm3.9 from repos

[pullmoll]

We no longer have a template for libllvm3.9 so we need to purge this package to get rid of staging. Also icecat should be purged as it can not be built with current rust and is quite outdated anyway.

[Chocimier]

I guess this is the issue @the-maldridge refers to as "shlibs problems" in defend of emptying packages over dropping template. If so, automatically unindexing packages with dropped template solves this issue as well.

[the-maldridge]

This is one of a handful of issues, but is the most pressing one. It is 1AM here so I don't trust myself to run commands against the builders as root and not screw something up, but I'll handle it in the morning if no-one has gotten to it by then.

I'm not 100% sure the linked PR is safe in all cases, so I'd like to review further before adopting it as the solution for the future. I do however think that intent based packaging is probably the way to go. Ideally it would check intent in both directions and handle missing packages as well.

[Duncaen]

Removed both.

[pullmoll]

Merci.