Remove Cone shape from particle emitters

[iche033]

🦟 Bug fix

Summary

Cone shape particle emitters are not supported in gz yet. We should add this only when there is support for it, see https://github.com/gazebosim/gz-rendering/pull/1003#pullrequestreview-2082665533

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)
• [ ] 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.

[iche033]

cc @bperseghetti

[bperseghetti]

cc @bperseghetti

@azeey guess I don't have reviewer permissions on this repo......