Remove the room list notification count feature flag.

The room list now always shows the unread notification count for highlighted rooms
and the app icon badge always uses the SDK's own unread notification count, both in
the app and in the NSE. The push payload's unread count is no longer used, so its
UNNotificationContent helper and user info key have been removed along with the
setting, its developer options toggle and the feature-disabled unit test.

UnitTests/Sources/NotificationManager/NotificationManagerTests.swift

@@ -240,7 +240,6 @@ final class NotificationManagerTests {
     
     @Test
     func updatingAppBadgeCountUsesTheClientSideCount() async {
-        appSettings.roomListNotificationCountEnabled = true
         clientProxy.totalUnreadNotifications = 7
         
         await notificationManager.updateAppBadgeCount()
@@ -251,23 +250,12 @@ final class NotificationManagerTests {
     
     @Test
     func updatingAppBadgeCountWithoutASessionDoesNothing() async {
-        appSettings.roomListNotificationCountEnabled = true
         notificationManager.setUserSession(nil)
         
         await notificationManager.updateAppBadgeCount()
         
         #expect(!notificationCenter.setBadgeCountCalled)
     }
-    
-    @Test
-    func updatingAppBadgeCountWithFeatureDisabledDoesNothing() async {
-        appSettings.roomListNotificationCountEnabled = false
-        clientProxy.totalUnreadNotifications = 7
-        
-        await notificationManager.updateAppBadgeCount()
-        
-        #expect(!notificationCenter.setBadgeCountCalled)
-    }
 }
 
 extension NotificationManagerTests: @MainActor NotificationManagerDelegate {