Do not include source .mojom files in dart pkgs
Do not include source .mojom files in dart pkgs

I've heard from blundell@ that the plan is to not include these.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1155283005

chinmaygarde/mojo,chinmaygarde/mojo,afandria/mojo,afandria/mojo,chinmaygarde/mojo,afandria/mojo,chinmaygarde/mojo,jianglu/mojo,afandria/mojo,afandria/mojo,jianglu/mojo,chinmaygarde/mojo,chinmaygarde/mojo,chinmaygarde/mojo,jianglu/mojo,jianglu/mojo,chinmaygarde/mojo,jianglu/mojo,afandria/mojo,jianglu/mojo,jianglu/mojo,chinmaygarde/mojo,afandria/mojo,afandria/mojo,jianglu/mojo