Don't remove deprecated fields like findbugsXmlOutput

Seems, that you removed the configuration setter findbugsXmlOutput in the 2.2 Snapshot version. It would be nice if you would only mark such fields (and setters) as deprecated and let them stay in the code forever, so that depending libraries need no code changes to function correctly (backward compatibility).

In my Hudson findbugs plugin I'm currently setting this value via an API call. That code now fails with an exception:
https://hudson.dev.java.net/issues/show_bug.cgi?id=4527

I'll add an exception wrapper in my code, so if you don't want to add the field again its ok for me. Just for the future it would be good to mark these changes as deprecated and show the users what to use instead of that method.