Fix EZP-23152: deleteVersion removes images from published version

JIRA: https://jira.ez.no/browse/EZP-23152

Image references are removed in the assumption there are no other field ids using it, which may not be true.
This adds a check for additional versions using the same id, and does not remove the reference in that case.
Actually, it should be `Checks if image $path can be removed when deleting $versionNo and $fieldId`.

How the method does it doesn't matter that much, the caller just wants to know if it can.