Remove scala-xml and scala-parser-combinators

These modules move to their own repositories:
  - https://github.com/scala/scala-xml
  - https://github.com/scala/scala-parser-combinators

The modularization depends on the new partest, as the old one's
classpath handling did not support a modularized scala.

The compiler pom now depends on the artifacts published separately,
with versions specified in versions.properties.

NOTES:
  - The osgi tests take xml and parsers jars from the scaladoc dependencies,
    and osgi-fy them, as they are no longer built locally.
  - Removed scala-partest-pom.xml. Should've been part of the partest move.