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/Application/Settings/AppSettings.swift

@@ -31,7 +31,6 @@ nonisolated protocol CommonSettingsProtocol: AnyObject, Sendable {
     var enableOnlySignedDeviceIsolationMode: Bool { get }
     var threadsEnabled: Bool { get }
     var hideQuietNotificationAlerts: Bool { get }
-    var roomListNotificationCountEnabled: Bool { get }
 }
 
 nonisolated enum AppBuildType {
@@ -358,9 +357,6 @@ final nonisolated class AppSettings: @unchecked Sendable {
     @UserPreference(defaultValue: RoomListActivityVisibility.current)
     var roomListActivityVisibility: RoomListActivityVisibility
     
-    @UserPreference(defaultValue: false)
-    var roomListNotificationCountEnabled: Bool
-    
     // MARK: - Search Screen
     
     /// The queries the user searched for and the rooms they opened from the results, most recent first.