Remove unsupported databases related metadata from the poms

Mainly in the xwiki-platform-distribution pom we have various metadata to help with generating the hibernate configuration file for various databases. But it does not make much sense to keep metadata (which kind of have recommendation values) for unsupported database, since nobody actually tested them in a very long time.

This includes the following:

• derby
• H2

If someone do use those in some custom XWiki distribution, it's easy to add them on their side.