Remove mojom copy step from dart_pkg.py script
Remove mojom copy step from dart_pkg.py script

BUG=
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1270573004 .

afandria/mojo,afandria/mojo,afandria/mojo,afandria/mojo,afandria/mojo,afandria/mojo,afandria/mojo,afandria/mojo