[llvm] [mlir] [CMake] Do not set CMP0116 explicitly to old (PR #90385)

[NAKAMURA Takumi via llvm-commits]

https://github.com/chapuni commented:

Let me reconfirm later. apparently looks good.

Note, when I introduced it, CMake didn't have `CMP0116 NEW` behavior.

https://github.com/llvm/llvm-project/pull/90385