Fix Motion examples package.json formatting and trailing comma

[AndrewJakubowicz]

Issue

Motion package.json samples have:

{
  "dependencies": {
    "lit": "^2.0.0",
    "@lit-labs/motion": "^1.0.1",  }
}

Which result in error: Invalid package.json: SyntaxError: Expected double-quoted property name in JSON at position 78.

Repro at: https://lit.dev/playground/#sample=examples/motion-list

Fix

Remove trailing comma.

Testing

This is a tidy up change as there was no user facing impact (unless they created a package.json). Tested manually by checking the motion samples still work locally.

[github-actions]

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https://pr1129-504d397---lit-dev-5ftespv5na-uc.a.run.app/

[augustjk]

Thank you!