Removing deprecated ios/web/user_metrics.cc and references to it.

ios/web/public/user_metrics.h

-// Copyright 2014 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 IOS_WEB_PUBLIC_USER_METRICS_H_
-#define IOS_WEB_PUBLIC_USER_METRICS_H_
-
-#include <string>
-
-#include "base/callback.h"
-
-namespace base {
-struct UserMetricsAction;
-}  // namespace base
-
-namespace web {
-
-// Wrappers around functions defined in base/metrics/user_metrics.h, refer to
-// that header for full documentation. These wrappers can be called from any
-// thread (they will post back to the UI thread to do the recording).
-
-void RecordAction(const base::UserMetricsAction& action);
-void RecordComputedAction(const std::string& action);
-
-}  // namespace web
-
-#endif  // IOS_WEB_PUBLIC_USER_METRICS_H_