`hs60/v2/hhkb`: Adjust layout name

[fauxpark]

Description

Investigating this warning which confused me as 60_hhkb is a valid community layout which should not be factored in: ⚠ hs60/v2/hhkb: Layout "LAYOUT_60_hhkb" should not contain name of keyboard.

As far as the layouts/ directory is concerned this is not an HHKB layout, which explains the warning as it is not tagged in community_layouts (thus the keyboard name itself is also incorrect).

Types of Changes

• [ ] Core
• [x] Bugfix
• [ ] New feature
• [x] Enhancement/optimization
• [x] Keyboard (addition or update)
• [x] Keymap/layout/userspace (addition or update)
• [ ] Documentation

Issues Fixed or Closed by This PR

Checklist

• [x] My code follows the code style of this project: C, Python
• [x] I have read the PR Checklist document and have made the appropriate changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] I have tested the changes and verified that they work and don't break anything (as well as I can manage).