Get rid of hardwired Xerces dependency

The Reengineer modules include two instances of Xerces:

• reengineer.xerces has a dependency on xercesImpl-2.7.1 and re-exports it.
• reengineer.xml bundles a xercesImpl-2.7.1 jar and includes it in its classpath, yet it also depends on reengineer.xerces

No other bundle dependes on reengineer.xerces

Remove reengineer.xerces from the build cycle. If we want to make sure reengineer.xml uses a specific version of xercesImpl, do so in the reengineer.xml POM without re-exporting the Xerces packages. We can also use the Embed-Dependency instruction.