base: Erase unused FOR_EACH_OBSERVER macro.

base/observer_list.h

 // Copyright (c) 2011 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_OBSERVER_LIST_H_
 #define BASE_OBSERVER_LIST_H_
 
 #include <stddef.h>
 
 #include <algorithm>
@@ skipping 326 matching lines @@
       ObserverListBase<ObserverType>::Compact();
       DCHECK_EQ(ObserverListBase<ObserverType>::size(), 0U);
     }
   }
 
   bool might_have_observers() const {
     return ObserverListBase<ObserverType>::size() != 0;
   }
 };
 
-// Deprecated. Use the range-based for loop instead.
-#define FOR_EACH_OBSERVER(ObserverType, observer_list, func) \
-  do {                                                       \
-    for (ObserverType & o : observer_list)                   \
-      o.func;                                                \
-  } while (0)
-
 }  // namespace base
 
 #endif  // BASE_OBSERVER_LIST_H_