c2e3e91dde
This is a follow-up of https://reviews.llvm.org/D125832 (see also https://reviews.llvm.org/D125788 for more context). It simply removes any remaining references to the `flang` bash script. Note that that `flang-to-external-fc` remains intact. This felt worthwhile mentioning in the release notes, which have not been updated since LLVM 12 (we are approaching LLVM 15 now). I took the liberty of removing all of the out-dated content and added a note about the renaming. Differential Revision: https://reviews.llvm.org/D127094