notif [nfc]: Encapsulate registerToken a bit more

This logic is about the token, and this is the class that tracks
the token in the first place, so the logic might as well live here
on this class.

Author: gnprice

lib/model/store.dart

@@ -1522,9 +1522,7 @@ class UpdateMachine {
   }
 
   Future<void> _registerNotificationToken() async {
-    final token = NotificationService.instance.token.value;
-    if (token == null) return;
-    await NotificationService.registerToken(store.connection, token: token);
+    await NotificationService.instance.registerToken(store.connection);
   }
 
   /// Cleans up resources and tells the instance not to make new API requests.

lib/notifications/receive.dart

@@ -147,7 +147,10 @@ class NotificationService {
     token.value = value;
   }
 
-  static Future<void> registerToken(ApiConnection connection, {required String token}) async {
+  Future<void> registerToken(ApiConnection connection) async {
+    final token = this.token.value;
+    if (token == null) return;
+
     switch (defaultTargetPlatform) {
       case TargetPlatform.android:
         await addFcmToken(connection, token: token);