Exclude the extraneous xmlpull and xpp3_min dependencies in jenkins-core.

The xpp3_min artifact causes a "JBAS015893: Encountered invalid class name" error on deployment in JBoss AS7 due to a malformed manifest in the artifact. The xpp3 artifact is extraneous since the xpp3 library is a direct dependency for jenkins-core. The xpp3 library replaces the xmlpull library.