Cleaned up launch file example_1/rrbot.launch.py (backport #959)

[mergify]

Addresses #950 by cleaning up a single launch file: example_1/rrbot.launch.py. This file has been improved to use a declarative programming style, as described by @emersonknapp at ROSCon, which can be viewed in the livestream at 6:10. A couple of local variables are needed for the Event Handlers, but all other unnecessary local variables are removed.

This change is a draft PR for feedback before rolling out changes to other launch files in other examples.

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This is an automatic backport of pull request #959 done by Mergify.

[mergify]

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