Remove some commented out code.
Update JastAdd to 2.1.9.

Some small fixes to make:
* One place in the code used "new Stmt() {}" but this doesn't work
anymore Stmt is an abstract class with unimplemented methods -- replaced
with "new AssignStmt()".
* The ant task has a different name and expects rewrite="regular"
instead of rewrite="true".
Move AstUtil methods into aspects.

JastAdd 2.1.9 added support for generic inter-type declarations [0], so
there's no need to define them outside the aspects. It doesn't yet
support Java 8 though, so revert them to pre-Java-8 form.

[0]: https://bitbucket.org/jastadd/jastadd2/issue/183/syntax-error-when-declaring-generic