cask: remove os_versions

[apainintheneck]

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Fixes #15227.

Overview

This was originally used by the API but was replaced months ago by SimulateSystem. Essentially, it's only current use was in the Cask::Cask#to_h method but is not used internally at all when creating cask instances from the API JSON.

Details

It was added to brew in #11915 and added to the formulae.brew.sh website in Homebrew/formulae.brew.sh#539. The use in the formulae.brew.sh website was later removed in Homebrew/formulae.brew.sh@b5704d4 so the only remaining references are in the main brew repo.

The Cask::Cask#os_versions method was only called in Cask::Cask#to_h to create the versions field in the JSON representation. It is not referenced at all in Cask::CaskLoader so isn't needed when loading cask instances from the JSON.

An added bonus is that removing this will speed up JSON generation a lot. It was very slow before because it required reloading casks a bunch of times.

Before

After

I also updated some test fixtures to remove the versions field.

[MikeMcQuaid]

Very nice, thanks again @apainintheneck!