Comment 20 for bug 1582515

Tested in an up-to-date xenial system:
- Enabled the proposed archive
- Updated snapcraft to 2.10
- Made a snapcraft dir.
- snapcraft strip
- The step is executed and a deprecated message is printed.
- snapcraft clean
- snapcraft prime
- The step is executed and no deprecated message is printed.
- snapcraft strip
- The step is not executed again.
- snapcraft prime
- The step is not executed again.
- snapcraft clean -s prime
- The step is cleaned.
- snapcraft clean -s strip.
- Got an error message because the step is not valid. This is a bug, because the deprecation message should be printed here too. Reported in https://bugs.launchpad.net/snapcraft/+bug/1590256

We can fix this in the next release, so I'm marking the verification as done.

Thanks Chris!