Remove test.py flags from builders in test_matrix, use configuration instead.
Remove test.py flags from builders in test_matrix, use configuration instead.

The -n<named configuration> flag is being used instead of the
command-line flags in the test.py builder steps.  Remove the unused flags.

Bug: https://github.com/dart-lang/sdk/issues/34066
Change-Id: I07a451273741618e23f85e900eac040e29c84c0a
Reviewed-on: https://dart-review.googlesource.com/69970
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@google.com>

dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk