Remove turtlebot3 packages from .rosinstall

[mm318]

Description of changes:

In the same vein as https://github.com/aws-robotics/aws-robomaker-sample-application-cloudwatch/pull/67 and https://github.com/aws-robotics/aws-robomaker-sample-application-persondetection/pull/66, this removes turtlebot3 packages from the .rosinstall file, so that these packages are no longer obtained by source code through rosws update, but rather directly by binary through rosdep install, which should be the preferred method.

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[mm318]

I will additionally do manual testing on RoboMaker simulation.