Do not include void into mocked method arguments

If a function that takes no arguments explicitly states (void)
then do not include it in the mocked method argument list
since it triggers static assertions that expect no arguments
to be present.

Fixes (?) #3261

googlemock/scripts/generator/cpp/gmock_class_test.py

@@ -156,7 +156,7 @@ class Foo {
 };
 """
     self.assertEqualIgnoreLeadingWhitespace(
-        'MOCK_METHOD(int, Bar, (void), (override));',
+        'MOCK_METHOD(int, Bar, (), (override));',
         self.GenerateMethodSource(source))
 
   def testStrangeNewlineInParameter(self):