thruster test: remove unnecessary sleep

[arjo129]

🦟 Bug fix

Fixes #

Summary

I'm not why this sleep was here in the first place. But it does not seem to be needed. The only thing it does is slow down our tests.

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

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[arjo129]

@osrf-jenkins run tests please