api: Drop isOwner, isAdmin, isGuest from User class

These are obsoleted by [User.role] (which dates to Zulip 4.0).
We never looked at these fields, but had a latent bug because
we weren't keeping them up to date on RealmUserUpdateEvent.
To fix the bug, just stop having the fields around at all.

(Later if we find we want booleans with these handy names,
we can always add getters that just inspect [User.role].)

lib/api/model/model.dart

@@ -194,9 +194,9 @@ class User {
   String fullName;
   String dateJoined;
   bool isActive; // Really sometimes absent in /register, but we normalize that away; see [InitialSnapshot.realmUsers].
-  bool isOwner;
-  bool isAdmin;
-  bool isGuest;
+  // bool isOwner; // obsoleted by [role]; ignore
+  // bool isAdmin; // obsoleted by [role]; ignore
+  // bool isGuest; // obsoleted by [role]; ignore
   bool? isBillingAdmin; // TODO(server-5)
   bool isBot;
   int? botType; // TODO enum
@@ -240,9 +240,6 @@ class User {
     required this.fullName,
     required this.dateJoined,
     required this.isActive,
-    required this.isOwner,
-    required this.isAdmin,
-    required this.isGuest,
     required this.isBillingAdmin,
     required this.isBot,
     required this.botType,

test/api/model/model_checks.dart

@@ -8,9 +8,6 @@ extension UserChecks on Subject<User> {
   Subject<String> get fullName => has((x) => x.fullName, 'fullName');
   Subject<String> get dateJoined => has((x) => x.dateJoined, 'dateJoined');
   Subject<bool> get isActive => has((x) => x.isActive, 'isActive');
-  Subject<bool> get isOwner => has((x) => x.isOwner, 'isOwner');
-  Subject<bool> get isAdmin => has((x) => x.isAdmin, 'isAdmin');
-  Subject<bool> get isGuest => has((x) => x.isGuest, 'isGuest');
   Subject<bool?> get isBillingAdmin => has((x) => x.isBillingAdmin, 'isBillingAdmin');
   Subject<bool> get isBot => has((x) => x.isBot, 'isBot');
   Subject<int?> get botType => has((x) => x.botType, 'botType');

test/example_data.dart

@@ -88,9 +88,6 @@ User user({
     fullName: fullName ?? 'A user', // TODO generate example names
     dateJoined: '2023-04-28',
     isActive: isActive ?? true,
-    isOwner: false,
-    isAdmin: false,
-    isGuest: false,
     isBillingAdmin: false,
     isBot: isBot ?? false,
     botType: null,