[llvm] [Flang][LLVM] Remove leftover CMake for old flang handling (PR #137049)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur requested changes to this pull request.

 * #130975 is for the dependencies for the LLVM_ENABLE_RUNTIMES=openmp build
 * This code deleted in this PR is for ensuring dependencies in the LLVM_ENABLE_PROJECTS=openmp build

Unless you entirely remove support for `LLVM_ENABLE_PROJECTS=openmp`, this code in this PR is still needeed.

https://github.com/llvm/llvm-project/pull/137049