api [nfc]: Require appid for addApnsToken route

This is required for current servers, since server-8.

The original binding for this route didn't mark it as required
because it was based on the reverse-engineered binding in
zulip-mobile, and that one hadn't been updated for server-8.
Now that the endpoint has API docs, we can use the information
they tell us.

Author: gnprice

lib/api/route/notifications.dart

@@ -13,10 +13,10 @@ Future<void> addFcmToken(ApiConnection connection, {
 /// https://zulip.com/api/add-apns-token
 Future<void> addApnsToken(ApiConnection connection, {
   required String token,
-  String? appid,
+  required String appid,
 }) {
   return connection.post('addApnsToken', (_) {}, 'users/me/apns_device_token', {
     'token': RawParameter(token),
-    if (appid != null) 'appid': RawParameter(appid),
+    'appid': RawParameter(appid),
   });
 }

test/api/route/notifications_test.dart

@@ -31,7 +31,7 @@ void main() {
   group('addApnsToken', () {
     Future<void> checkAddApnsToken(FakeApiConnection connection, {
       required String token,
-      required String? appid,
+      required String appid,
     }) async {
       connection.prepare(json: {});
       await addApnsToken(connection, token: token, appid: appid);
@@ -40,17 +40,11 @@ void main() {
         ..url.path.equals('/api/v1/users/me/apns_device_token')
         ..bodyFields.deepEquals({
           'token': token,
-          if (appid != null) 'appid': appid,
+          'appid': appid,
         });
     }
 
-    test('no appid', () {
-      return FakeApiConnection.with_((connection) async {
-        await checkAddApnsToken(connection, token: 'asdf', appid: null);
-      });
-    });
-
-    test('with appid', () {
+    test('smoke', () {
       return FakeApiConnection.with_((connection) async {
         await checkAddApnsToken(connection, token: 'asdf', appid: 'qwer');
       });