Improve scary container registry removal notification.

Summary

When an image is deleted on the .../container_registry/ page in GitLab UI, the following notification appears:

This container registry has been scheduled for deletion. 

which is scary and incorrect. It's a removal of a single docker image from the registry, but the message implies the whole registry is being wiped.

What is the expected correct behavior?

A more meaningful message would be something like:

Image 'xxx/yyy:latest' was scheduled for deletion from the registry.