isAnonymousClass/Function for delambdafy classes is not true

Ydelambdafy:method lambda classes are not anonymous classes, and not
anonymous function classes either. They are somethig new, so there's
a new predicate isDelambdafyFunction.

They are not anonymous classes (or functions) because anonymous
classes in Java speak are nested. Delambdafy classes are always
top-level, they are just synthetic.

Before this patch, isAnonymous was sometimes accidentailly true: if
the lambda is nested in an anonymous class. Now it's always false.

This should fix the [BCode-Delambdafy community build](https://jenkins-dbuild.typesafe.com:8499/job/Community-2.11.x-BCode-Delambdafy/125/console). An assertion in BCode failed because it was trying to emit an EnclosingMethod attribute for a delambdafy class - this should only happen for inner classes.