dartsim: To not call dart::collision::GzOdeCollisionDetector::create() in ConstructEmptyWorld

[traversaro]

🦟 Bug fix

Fixes problem described in https://github.com/gazebosim/gz-sim/issues/18#issuecomment-2301643365 .

Summary

Checklist

• [ ] Signed all commits for DCO
• [ ] Added tests
• [ ] 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)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[traversaro]

Unfortunately, this does not work as it is possible that one never calls the SetWorldCollisionDetector method.