code: function clearLocalDatabase() {
      idb.open('web-push-db', 1).then(db => {
          let tx = db.transaction(['web-push-subcription'], 'readwrite');
          tx.objectStore('web-push-subcription').clear();
          return tx.complete;
      });
  }
docs: Clears the local database (called after a user unsubscribes).