remove any lingering legacy notifications in modern notification adapter

Signal/src/UserInterface/Notifications/LegacyNotificationsAdaptee.swift

@@ -222,6 +222,10 @@ extension LegacyNotificationPresenterAdaptee: NotificationPresenterAdaptee {
         for (_, notification) in notifications {
             cancelNotification(notification)
         }
+        type(of: self).clearExistingNotifications()
+    }
+
+    public class func clearExistingNotifications() {
         // This will cancel all "scheduled" local notifications that haven't
         // been presented yet.
         UIApplication.shared.cancelAllLocalNotifications()

Signal/src/UserInterface/Notifications/UserNotificationsAdaptee.swift

@@ -181,6 +181,7 @@ extension UserNotificationPresenterAdaptee: NotificationPresenterAdaptee {
         AssertIsOnMainThread()
         notificationCenter.removeAllPendingNotificationRequests()
         notificationCenter.removeAllDeliveredNotifications()
+        LegacyNotificationPresenterAdaptee.clearExistingNotifications()
     }
 
     func shouldPresentNotification(category: AppNotificationCategory, userInfo: [AnyHashable: Any]) -> Bool {