rosdep: drop legacy Python 2 keys - Stage 4 (80%)

[mjcarroll]

Part of Python 2 drop. Links to #51715

[github-actions]

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For changes related to rosdep:

• ❌ There are problems with the names of new rosdep keys:
  • Keys which contain only pip rules should end in '-pip'
• ✅ Platforms for new rosdep rules are valid
• ❌ There are problems with explicitly provided installers:
  • One or more explicitly provided installer is not supported by rosdep
• ❌ There are problems with rosdep key suitability:
  • Rules exclusively for pip may not be added when there are system packages available
• 📝 Disclaimer: Pip-only rules cannot be used by packages on the ROS buildfarm

For changes related to yamllint:

• ✅ All new lines of YAML pass linter checks