Fixed announcement bar filtering for disabled members

refs https://github.com/TryGhost/Team/issues/3112

- When members features are disabled on the site, there is no point to show member-specific filters for the announcement bar. The only option available should be to show or not to show the announcement.

ghost/admin/app/components/announcement-settings/visibility.hbs

@@ -16,9 +16,14 @@
                     {{on "click" this.updateVisibility}}
                 >
                 <span class="input-toggle-component"></span>
+            {{#if this.isMembersEnabled}}
                 <span>Logged out visitors</span>
+            {{else}}
+                <span>Show the announcement</span>
+            {{/if}}
             </label>
 
+            {{#if this.isMembersEnabled}}
             {{#if this.isPaidAvailable}}
                 <label class="checkbox" for="free">
                     <input
@@ -60,6 +65,7 @@
                     <span>Members</span>
                 </label>
             {{/if}}
+            {{/if}}
         </div>
     </div>
 </div>

ghost/admin/app/components/announcement-settings/visibility.js

@@ -32,6 +32,10 @@ export default class AnnouncementSettingsVisibilityComponent extends Component {
         return this.visibilitySettings.includes(this.visibilityOptions.visitors);
     }
 
+    get isMembersEnabled() {
+        return this.settings.membersEnabled;
+    }
+
     @action
     updateVisibility(event) {
         let updatedVisibilityOptions = [...this.visibilitySettings];