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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Do you mean #130975?
> 
> LLVM_ENABLE_RUNTIMES=openmp and LLVM_ENABLE_PROJECTS=openmp are both still supposed to work. It just fixed a dependency problem with LLVM_ENABLE_RUNTIMES=openmp (and updates some CMake messages to clarify that there are two ways to build it.

Yeah, I figured that the only part we still needed was the dependency.

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