MJCF to SDFormat: Remove duplicate light added to the world

[azeey]

🦟 Bug fix

Summary

When there is a light directly under <worldbody>, we currently create a light in <world> and in the static model. This PR removes the light in <world>. We could remove the one in the static model, but this seemed like the easier option.

Checklist

• [x] 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)
• [x] 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.

[codecov[bot]]

Codecov Report

Merging #82 (8f07ab0) into main (b65298f) will decrease coverage by 0.02%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #82      +/-   ##
==========================================
- Coverage   95.16%   95.14%   -0.03%     
==========================================
  Files          24       24              
  Lines        1097     1092       -5     
==========================================
- Hits         1044     1039       -5     
  Misses         53       53              

Impacted Files	Coverage Δ
...sdformat_mjcf/mjcf_to_sdformat/converters/world.py	98.63% <ø> (-0.09%)	:arrow_down:

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