refactor: remove unused methods from RepositoryService and repository layer

[netomi]

What

RepositoryService had accumulated a number of public methods with no production caller - mostly superseded by later, more general query variants (e.g. findScansFiltered/countScansFiltered superseded by the *FullyFiltered versions, whose Page result already carries its own total) or left behind by earlier refactors.

Changes

• RepositoryService.java: removes 42 unused public methods, and makes hasMemberships(Namespace, String) private since it's now only used internally by isVerified().
• Repository layer: removing those delegates orphaned the underlying derived-query methods they called on the lower-level *Repository interfaces/classes in the same package. Removes 51 more unused methods across AdminScanDecisionRepository, ExtensionJooqRepository, ExtensionScanRepository, ExtensionThreatRepository, ExtensionValidationFailureRepository, ExtensionVersionJooqRepository, ExtensionVersionRepository, FileDecisionRepository, MigrationItemRepository, ScanCheckResultRepository, ScannerJobRepository, and UserDataRepository, plus their now-unused imports.
• MigrationItemJooqRepository: deleted outright - its one method was dead, and removing it left an empty class with no other purpose. Migration item discovery already goes through the generic findNotMigratedItems() path.
• Tests: trims the corresponding entries out of RepositoryServiceSmokeTest's exhaustive per-method coverage list, and drops two stale Mockito stubs in ScanAPITest/AdminAPITest for methods that no longer exist.

The other ~27 files in org.eclipse.openvsx.repositories were checked and had no unused methods.

Testing

Full ./gradlew test run: 1048 tests, 0 failures, 0 errors.

[netomi]

This PR removes any unused method in the RepositoryService and related Repository classes. Over the time various stuff has been added that is not needed anymore or never has been used. To keep things clean and easier to understand, remove everything this is currently not used.

Edit: most of the unused method are from the scan infrastructure, where no cleanup was ever done and the unused methods are mainly from some refactoring during the implementation of the feature in the first place.

[cstamas]

WOW