Should we bump the minimum SDK version?
Follow up from dart-lang/tools#489. We should consider bumping the minimum SDK version to 2.17, perhaps when bumping the coverage version to 3. This would let us remove the --packages flag, and all the extra code paths in the resolver, and give the user a less confusing error message.
There's also a bunch of other backwards compatibility code paths that could be removed. Eg some of the vm_service _versionCheck calls in collect.dart, and the related code paths. Also hitmapToJson, which is for backwards compatibility with super old SDKs.
One option - if we do want to continue to support some pre-2.17 sdks for a while - is to change the behavior of --packages to fast fail when run on 2.17 and later sdks.