[ios] Removed alloc_with_zone_interceptor as unused.

ios/web/alloc_with_zone_interceptor.mm

-// Copyright 2015 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.
-
-#import "ios/web/alloc_with_zone_interceptor.h"
-
-#import <objc/runtime.h>
-
-#include "base/logging.h"
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
-
-namespace web {
-
-void AddAllocWithZoneMethod(Class target, id (^impl_block)(Class, NSZone*)) {
-  // Make sure |allocWithZone:| is not already implemented in the target class.
-  Class meta_class = object_getClass(target);
-  DCHECK_EQ(
-      class_getMethodImplementation(meta_class, @selector(allocWithZone:)),
-      class_getMethodImplementation(object_getClass([NSObject class]),
-                                    @selector(allocWithZone:)));
-
-  IMP new_impl = imp_implementationWithBlock(^(id self, NSZone* zone) {
-    return impl_block(self, zone);
-  });
-  class_addMethod(meta_class, @selector(allocWithZone:), new_impl, "v@:@");
-}
-
-}  // namespace web