BREAKING CHANGE: Removes PubSubHubbub module and /hub API endpoint implementation

[mjimenez98]

Part of https://github.com/github/ecosystem-events/issues/3517

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Before the change?

• Octokit.rb is using the deprecated /hub endpoint through PubSubHubbub module. To expand on this deprecation, the comment at the top of lib/octokit/client/pub_sub_hubbub.rb includes a link to https://developer.github.com/v3/repos/hooks/#pubsubhubbub which no longer exists

After the change?

• Remove PubSubHubbub module. Webhooks API is accessible through the Hooks module, which uses the endpoints documented in GitHub's public docs

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[github-actions]

👋 Hi! Thank you for this contribution! Just to let you know, our GitHub SDK team does a round of issue and PR reviews twice a week, every Monday and Friday! We have a process in place for prioritizing and responding to your input. Because you are a part of this community please feel free to comment, add to, or pick up any issues/PRs that are labled with Status: Up for grabs. You & others like you are the reason all of this works! So thank you & happy coding! 🚀

[nickfloyd]

Thanks for the contributions here @mjimenez98 ❤️