Remove All-Contributors

[JasonEtco]

Why:

We've decided to remove the All Contributors bot. The frequency of community contributors, while awesome, has made maintaining the .allcontributorsrc file really difficult and time-consuming. The PRs it opens accumulate conflicts very quickly, and they're difficult to resolve.

We don't necessarily mean to remove it indefinitely - there are a couple of issues and feature requests (like all-contributors/app#62) that would help here. At least for now, we've decided to remove it until we're comfortable turning it back on. We still want to give credit to the community's contributions, we're just going to look for other ways to do so.

cc @janiceilene

What's being changed:

This PR removes the .allcontributorsrc file, the Contributors section from the README, and the prompt in the merged-notifications workflow.

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[janiceilene]

Thanks so much for opening this PR @JasonEtco! This looks good to go from a content perspective 💛

[nschonni]

Maybe keep this, and just point to https://github.com/github/docs/graphs/contributors

[JasonEtco]

Thanks for the suggestion @nschonni 🙏 I'm going to merge as-is, but feel free to open a followup PR if you'd like to add this!

[zeke]

We still want to give credit to the community's contributions, we're just going to look for other ways to do so.

👌🏼

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours.

If you haven't already, you can add yourself to the list of contributors by creating a new comment in this PR using these instructions. Thanks again! ✨