package.deprecated: Inform when the package is no longer used

[mgorny]

Suggested on IRC. Once all ebuilds stop depending on the deprecated package, it'd be nice to have another report telling us we can lastrite it already.

I suppose you'd want more caching first.

[radhermit]

Isn't this just https://github.com/pkgcore/pkgcheck/issues/11 reworded in a different fashion? :smile:

I've actually started designing a revdeps cache (https://github.com/pkgcore/pkgcheck/issues/285) format for that recently.