[nfc][compiler-rt]Replace Type::getInt8PtrTy with PointerType::getUnqual as a clean-up (#82434)

This is a follow up of
https://github.com/llvm/llvm-project/commit/7b9d73c2f90c0ed8497339a16fc39785349d9610
and
https://github.com/llvm/llvm-project/commit/5ef9ba74120dcc2da70ec25571d459f81ab8a705
* The definition of `Type::getInt8PtrTy` is deleted. This doesn't cause
a compile error because the `Initializer` part of the macro doesn't run.