Switches to package import for the dependency to osgi.service.location

The dependency to the bundle org.eclipse.osgi was creating conflict
with the bundle javax.xml.bind (included in Eclipse for JEE).

The problem was reported on the [mailing list](https://groups.google.com/d/msg/scala-ide-user/ZDeZ_rCX5BI/tr-ynGIgcMMJ).