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.

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/DeveloperOptionsScreenModels.swift

@@ -58,7 +58,6 @@ protocol DeveloperOptionsProtocol: AnyObject {
     var focusEventOnNotificationTap: Bool { get set }
     
     var roomListActivityVisibility: RoomListActivityVisibility { get set }
-    var roomListNotificationCountEnabled: Bool { get set }
     var elementCallBaseURLOverride: URL? { get set }
     
     var fuzzyRoomListSearchEnabled: Bool { get set }