Remove all references to Apache Derby

For a while, the Apache Derby embedded database is not used anymore by default, it was replaced by h2:

• at runtime, see https://github.com/nuxeo/nuxeo/blob/10.10/nuxeo-distribution/nuxeo-nxr-server/src/main/resources/templates/default/nuxeo.defaults
• in the unit test framework, see https://github.com/nuxeo/nuxeo/blob/10.10/nuxeo-core/nuxeo-core-storage-sql/nuxeo-core-storage-sql-test/src/main/java/org/nuxeo/ecm/core/storage/sql/DatabaseHelper.java#L48

Let's get rid of Derby:

• in the code
• in the documentation

This must be mentioned as upgrade notes.