Update test_flake8.py files
As of Foxy there's a new function in ament_flake8.main
which allows the test to print the errors directly: https://github.com/ament/ament_lint/pull/221
The test_flake8.py
files should simply be replaced by: https://github.com/ros2/launch/blob/4370b2b829946cd8c5ec5a76cbb3bb6a70c95e97/launch/test/test_flake8.py