[systemconfiguration] Small update for iOS 10 beta 1 (#312)

It looks like Apple reverted the deprecation of the API (maybe due to
lack of alternatives for some?)

src/SystemConfiguration/CaptiveNetwork.cs

@@ -19,7 +19,6 @@ namespace XamCore.SystemConfiguration {
 	
 	// http://developer.apple.com/library/ios/#documentation/SystemConfiguration/Reference/CaptiveNetworkRef/Reference/reference.html
 	// CaptiveNetwork.h
-	[Availability (Deprecated = Platform.iOS_9_0, Message = "Use NEHotspotHelper")]
 	public static partial class CaptiveNetwork {
 		
 #if !MONOMAC