Extension updater propose upgrades for optional dependencies

Extension Updater is supposed to only search for updates of top level extension and not try dependency to avoid bad surprises. An exception to that rule is extensions which don't have any backward dependencies, the problem is that the upgrade job use the wrong API and find no backward dependency for optional dependencies.

To reproduce:

• start jetty+hsqldb 12.10.5
• ask for updates of extensions

-> you end up with various proposals while there should not be any