Observation reference is lost when project is removed

[miketheman]

If an observation is created, and the underlying project is removed, the observation (intentionally) becomes orphaned. This was generally chosen for long-term persistence.

However, in the resulting email communication, the links lead to an effectively "empty" page for any reports for the given project, as the reference ID is no longer available.
If the project is then recreated/uploaded to PyPI, there's still a project, but it'll have a new ID.

I'm not sure how this should be fixed yet - it's now happened one time, so I wanted to capture it while it was fresh in mind.

[miketheman]

Related: When trying to add an action/verdict to this kind of observation raises an AttributeError:
https://python-software-foundation.sentry.io/share/issue/d4149ee5cc434af588da743308ed08ae/