Delete details snapshot on backup delete (#2166)

## Description

Don't leave orphaned details snapshots when a backup is being deleted.

## Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No 

## Type of change

- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Test
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

## Issue(s)

* closes #2152

## Test Plan

- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

src/pkg/repository/repository.go

@@ -325,6 +325,10 @@ func (r repository) DeleteBackup(ctx context.Context, id model.StableID) error {
 		return err
 	}
 
+	if err := r.dataLayer.DeleteSnapshot(ctx, bu.DetailsID); err != nil {
+		return err
+	}
+
 	sw := store.NewKopiaStore(r.modelStore)
 
 	return sw.DeleteBackup(ctx, id)