Remove Cuba from domain fronting.

Google hosted domain fronting doesn't work in Cuba due to export
restrictions. OTOH there are reports of Signal working just fine without
domain fronting in Cuba.

// FREEBIE

src/Network/OWSCensorshipConfiguration.m

@@ -1,5 +1,6 @@
-// Created by Michael Kirk on 12/20/16.
-// Copyright © 2016 Open Whisper Systems. All rights reserved.
+//
+//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//
 
 #import "OWSCensorshipConfiguration.h"
 #import "TSStorageManager.h"
@@ -52,8 +53,6 @@ NSString *const OWSCensorshipConfigurationReflectorHost = @"signal-reflector-mee
     return @{
              // Egypt
              @"+20": @"google.com.eg",
-             // Cuba
-             @"+53": @"google.com.cu",
              // Oman
              @"+968": @"google.com.om",
              // UAE