Delete jsonnet dead code

[ArthurSens]

Keeping dead code around brings absolutely 0 benefits. It makes git operations slower, but most importantly: It causes confusion to people that navigate through this repository but not as often as the usual maintainers.

Since we switched to our own installer written in go, most of our jsonnet code has become dead code. We still use it here and there for monitoring-central, grafana and CRDs. We should remove everything else