Revert WeavingAdaptor generated class map optimisation

Revert WeavingAdaptor generated class map optimisation

This was introduced in commit 8a4aa03845 of PR #278 contribution as part
of the #279 fix. The contributor thought that the generated closure
class entries were never used, but in fact AJDT class OSGiWeavingAdaptor
relies on the presence of those entries.

To the best of my present knowledge, it looks as if this change was the
root cause of https://github.com/eclipse-aspectj/ajdt/issues/57.
Therefore, I reverted it, simultaneously refactoring Iterator::remove
usage to delete entries from the map to Collection::removeIf.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>