phantomjs: remove and migrate to cask

[bval]

This works in conjunction with Homebrew/homebrew-cask#52595 to migrate phantomjs over to a Cask. This is detailed in #32402.

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• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

[fxcoudert]

Error: Missing formulae should not have dependents!
asciinema2gif
casperjs

Both are simple javascript files that depend on phantomjs. Not sure what to do…

[bval]

asciinema2gif

asciinema2gif has 48 installs in 30 days, no commits in 2 years, and is simple enough to clone for the handful of people using it. Maybe safe to nuke?

casperjs

casperjs is unmaintained. It's also available via npm for those who still need it. Perhaps it's safe to remove from core? Current stats show 341 installs in 30 days, which is not nothing, but is relatively small.

If I get a 👍 I will update the PR to nuke those 2 formulae as well.

[fxcoudert]

I don't see another way forward

[commitay]

Thanks @bval!