Remove unnecessary code, clarify usage for unclear code

[fwc]

For me personally, some code (e.g. install-llvm-host.sh and original-build-script) seems superfluous to me.

I propose we remove this code, if it is unnecessary.
If it is still needed, but necessity is difficult to spot (like e.g. with the rocky-linux dependencies, which aren't consumed by our main build, I propose we add comments detailing the need.