Revisit calculate repository

[AMDmi3]

What we currently have as 'calculate' is actually calculate overlay with a handful of packages, not actual calculate repository of prebuilt gentoo packages. Packagelinks are not even correct, despite calculate repository includes packages from the overlay.

Actual calculate packages information is available at https://mirror.yandex.ru/calculate/grp/x86_64/Packages.xz, but it lacks required homepage information.

Practical solution would be to remove calculate, since we cannot add real repository, and we don't really want overlays.