[CIR][NFC] Fix memory corruption in type converter (llvm#160211)

This fixes a problem where a rogue call to converter.addConversion
inside of a type conversion lambda was causing memory corruption that
(luckily!) triggered a test failure on some build platforms.

Near as I can tell, the unwanted addConversion call was the result of a
bad rebase (by me). The code shouldn't have ever been there. Because the
failure depends on the build environment, I can't find a reliable way to
test this change.

Author: andykaylor

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -2381,9 +2381,6 @@ static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
       }
       break;
     }
-    converter.addConversion([&](cir::VoidType type) -> mlir::Type {
-      return mlir::LLVM::LLVMVoidType::get(type.getContext());
-    });
 
     // Record has a name: lower as an identified record.
     mlir::LLVM::LLVMStructType llvmStruct;