Delete irrelevant snapshots on test-plan run to match generated code

[EduardJelenski]

Context 🕵️‍♀️

If you had previews set up earlier and now store generated snapshots, then decided to remove previews for some reason, the snapshots stay stored

What 🌱

I think it may be confusing for developers

Proposal 🎉

I think snapshots should work similar to test-plans code generator, which doesn't generate the lines of code for previews you have deleted.

[BarredEwe]

Thanks for the suggestion! This could be a cool feature. I would suggest to make this improvement at the level of swift-snapshot-testing library, as it is responsible for all snapshot logic inside Prefire.