Remove @@ tags and "future" notes

[Cito]

Sprinkled throughout the code are comments tagged with @@ which are hopefully accompanied by a date and someone's initials. These comments represent things to be done. The double at-sign (@@) convention was chosen because it doesn't appear to be used for anything else.

There are also "FUTURE" items mentioned in class doc strings and comments.

Remove any such comments, since w4py2 will not be developed further, or create w4py3 issues on GitHub if changes are still desirable.