Revert "[flang] Improve debug info for functions." (#90444)

Reverts llvm/llvm-project#90083 due to a test suite failure:
https://lab.llvm.org/buildbot/#/builders/184/builds/11961

```
flang-new: ../llvm/mlir/lib/IR/Types.cpp:126: unsigned int mlir::Type::getIntOrFloatBitWidth() const: Assertion `isIntOrFloat() && "only integers and floats have a bitwidth"' failed.
```