Remove all ignition references on ROS 2 branch

[mjcarroll]

🎉 New feature

Summary

This completes the migration:

• Remove ros_ign shims
• Remove ignition headers
• Remove ignition.msgs references

Note: Once merged, the ros2 branch will only support collections that have the full renaming applied (at this time garden only)

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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