Add "museum" page for discontinued brands

[jorgeamadosoria]

As time passes, some brands disappear and are removed from the library. This represents a backwards compatibility problem with users that have these icons but keep their dependencies updated.

This is only an issue for brands or icons that are removed due to falling popularity or outright disappearing. Not every removal qualifies for this, for example:

• Brands that are added by mistake or whose guidelines change after being added in such a manner as to preclude them from being used (Fedora icon, for example). In these cases a backwards break is acceptable since it would force the user to forgo a trademark violation.
• Brands that are updated due to changing design (Google trademarks changes fairly frequently). The updated design would substitute the old one, which is a minor issue, only affecting the display of historically significant icon lists, which is not the goal of this library anyways.
• Changes in name or slug. This will introduce a backwards compatibility issue, but since the icon is not changed nor removed, the icon won't qualify to be conserved: it's still live in the main repo.

A potential solution for this is a list page with the removed icons, similar to the existing main page but without the features for sorting or copying, etc. A minimal page would just list all removed SVGs so the user can potentially download it and use it manually or at most offer a permanent link to the latest version in which the icon can be found.

The page would have to be manually updated on each release to add the icons removed, of course.

[jorgeamadosoria]

After making a proposal in the linked PR, I think the effort necessary to automate and maintain this page is too high for the perceived benefit. As such, I'm closing this ticket as unnecessary, since no other maintainer has expressed interest in moving it forward either.

[mondeja]

This can be rethinked if something like https://github.com/simple-icons/simple-icons/issues/7437 is implemented.