api: Update Subscription for api changes

Remove `emailAddress` field per update in FL 266. Also
changed `isWebPublic` to be non-null. It has been a
field on subscriptions since at least FL 8 (see
zulip/zulip@f93c19ec6 in `zerver/openapi/zulip.yaml`
and `gather_subscriptions_helper` in `zerver/lib/actions.py`).

Author: sirpengi

lib/api/model/model.dart

@@ -326,14 +326,13 @@ class Subscription {
   final int? streamWeeklyTraffic;
 
   final bool inviteOnly;
-  final bool? isWebPublic; // TODO(server-??): doc doesn't say when added
+  final bool isWebPublic;
   final bool historyPublicToSubscribers;
   final int? messageRetentionDays;
   // final List<int> subscribers; // we register with includeSubscribers false
 
   final StreamPostPolicy streamPostPolicy;
   // final bool? isAnnouncementOnly; // deprecated for `streamPostPolicy`; ignore
-  final String emailAddress;
 
   final int? canRemoveSubscribersGroupId; // TODO(server-6)
 
@@ -366,7 +365,6 @@ class Subscription {
     required this.pushNotifications,
     required this.audibleNotifications,
     required this.pinToTop,
-    required this.emailAddress,
     required this.isMuted,
     required this.isWebPublic,
     required this.color,