docs: remove pr title extension advice

[zpeterson]

Pull Request

📖 Description

Remove the suggestion that contributors use Refined GitHub or Squashed Merge Message because Squashed Merge Message pointed to GitHub's solution for this issue: New options for controlling the default commit message when merging a pull request.

🎫 Issues

None.

👩‍💻 Reviewer Notes

A maintainer/admin with perms to update the repo settings will need to make the update outlined in New options for controlling the default commit message when merging a pull request.

📑 Test Plan

Test default commit message after making the settings update.

✅ Checklist

N/A -- no code change

General

• I have included a change request file using $ yarn change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Component-specific

• I have added a new component
• I have modified an existing component
• I have updated the definition file
• I have updated the configuration file

[janechu]

Thanks for this! We're doing an overhaul of our docs so this ran into some conflicts, I've included your changes here: 04d2296