Deprecate (and no longer use) IRepositoryIndexer / IRepositoryDiscoverer

[laeubi]

On my journey about rework IMavenProjectFacade I stumbled over some usages of methods requiring a project because of notification of IRepositoryIndexer this seems a left-over that is effectively nowhere used in m2e. The indexers are notified about added/removed repositories but nothing else happens.

My idea is therefor to deprecate the IRepositoryIndexer interface and remove the remaining usages. The same also seem to apply to IRepositoryDiscoverer ... but probably someone knows more about the history and what this is/was useful for?

[mickaelistria]

I guess it was used back then when using Maven index to detect artifacts. I don't think it will be missed if you remove them.