Remove base::NonThreadSafe now that all users are gone!!

base/ios/weak_nsobject.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_IOS_WEAK_NSOBJECT_H_
 #define BASE_IOS_WEAK_NSOBJECT_H_
 
 #import <Foundation/Foundation.h>
 #import <objc/runtime.h>
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
-#include "base/threading/non_thread_safe.h"
 #include "base/threading/thread_checker.h"
 
 // WeakNSObject<> is patterned after scoped_nsobject<>, but instead of
 // maintaining ownership of an NSObject subclass object, it will nil itself out
 // when the object is deallocated.
 //
 // WeakNSProtocol<> has the same behavior as WeakNSObject, but can be used
 // with protocols.
 //
 // Example usage (base::WeakNSObject<T>):
@@ skipping 154 matching lines @@
 
   WeakNSObject& operator=(const WeakNSObject<id>& that) {
     WeakNSProtocol<id>::operator=(that);
     return *this;
   }
 };
 
 }  // namespace base
 
 #endif  // BASE_IOS_WEAK_NSOBJECT_H_