Print deleted digest when repo tags empty

[thomasf7]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR updates the crictl rmi command to print the repoDigests of deleted images where the image has no repoTags, which can happen when the image digest is used for pulling the image. Currently when this happens the images are deleted with no output whatsoever to indicate this has happened.

Which issue(s) this PR fixes:

Fixes #976

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Added output to `crictl rmi` when deleting images that were pulled by digest and therefore have no tags.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: thomasf7 / name: Thomas Faulkner (a07c04e)

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[saschagrunert]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: saschagrunert, thomasf7

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