ci: remove apple intel builds

[galargh]

Related Issues

CircleCI is removing support for Apple Intel executors on Oct 2 - see https://discuss.circleci.com/t/macos-resource-deprecation-update/46891. After that date only Apple Silicon executors will be available. This PR removes CircleCI jobs that were using Apple Intel executors.

Proposed Changes

To remove CircleCI jobs that are using Apple Intel executors.

Additional Info

https://discuss.circleci.com/t/macos-resource-deprecation-update/46891

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, build, chore, ci, docs, perf, refactor, revert, style, test
  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
• If the PR affects users (e.g., new feature, bug fix, system requirements change), update the CHANGELOG.md and add details to the UNRELEASED section.
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green

[galargh]

As per filecoin-project/rust-fil-proofs#1722 (comment), it turns out I misunderstood the announcement (timeline) slightly. I'm going to close this PR now and recreate it with correct commit messages and description. I'm sorry for the extra noise.