Simplify comparison against CustomCppVoidType::TypeId.

Author: bricknerb

toolchain/check/cpp/type_mapping.cpp

@@ -186,8 +186,7 @@ static auto MapNonWrapperType(Context& context, SemIR::InstId inst_id,
 static auto TryMapVoidPointer(Context& context, SemIR::TypeId type_id,
                               llvm::SmallVector<SemIR::TypeId>& wrapper_types)
     -> clang::QualType {
-  if (context.types().Is<SemIR::CustomCppVoidType>(type_id) &&
-      !wrapper_types.empty() &&
+  if (type_id == SemIR::CustomCppVoidType::TypeId && !wrapper_types.empty() &&
       context.types().Is<SemIR::PointerType>(wrapper_types.back())) {
     wrapper_types.pop_back();
     return context.ast_context().getAttributedType(