We added logic to produce the new packages file: .dart_tool/package_config.json, however we now generate both that and .packages. I think we should stop generating .packages, so that there is a single master, and less room for confusion.

Known dependants of the .packages file that will need to get fixed first:

• dart.dev docs: Migrate documentation from .packages to .dart_tools/package_config.json site-www#3422
• IntelliJ plugin: The .packages file is obsolete and should not be used flutter/flutter-intellij#5614