Bug: Debug in migrate doesn't remove the property as expected

[evenstensberg]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
Running migrate on a config that has debug doesn't remove debug after adding it to commonsChunk if there is any.

If the current behavior is a bug, please provide the steps to reproduce.
What is the expected behavior?

Migrate this https://gist.github.com/ev1stensberg/28bb27feda110e57c079b9597ee4d07f
Should turn into this: https://gist.github.com/ev1stensberg/bff1da6851d81844de76c736d2fc566d

If this is a feature request, what is motivation or use case for changing the behavior?
No
Please mention other relevant information such as the browser version, Node.js version, Operating System and programming language.

[webpack-bot]

This issue had no activity for at least half a year.

It's subject to automatic issue closing if there is no activity in the next 15 days.

[webpack-bot]

Issue was closed because of inactivity.

If you think this is still a valid issue, please file a new issue with additional information.

[evenstensberg]

Still an error, so let's keep this open