sqlite: drop catalog_test.go

The end-to-end tests cover the catalog the schema builds. Removing the
test leaves newTestCatalog with no callers, so it goes too.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RkrYmzwTktB2CA5Bvqg6z5

Author: claude

internal/engine/sqlite/catalog.go

@@ -12,7 +12,3 @@ func NewCatalog() *catalog.Catalog {
 		Extensions: map[string]struct{}{},
 	}
 }
-
-func newTestCatalog() *catalog.Catalog {
-	return catalog.New("main")
-}