Skaffold artifact cache should not include image-name in hash calculation

[briandealwis]

The container-debug-support images are published using two sets of names: a short-form like go as well as a longer-form like skaffold-debug-go. This is done with a profile using JSONPatch. The idea was that long-form and short-form images can be built and published using:

skaffold build                        # step 1: build and push with long-form names
skaffold build -p deprecated-names    # step 2: build and push with short-form names

In step 2, Skaffold's artifact caching should detect that there are no source changes and simply re-push the image from step 1.

This no longer works, and instead step 2 builds the images. I suspect we must be using the build.artifacts[].image as part of the artifact hash calculation.