docker-machine-driver-xhyve: deprecate

[andig]

• 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?
• Is your test running fine brew test <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>)?

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Get go1.15.6 merged in #66355

[azure-pipelines]

There was an error handling pipeline event efa03bb9-25b7-4de1-b41b-255c17ebc099.