tools/gn: Remove code for forward_dependent_configs_from variable.

tools/gn/variables.h

 // Copyright (c) 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 TOOLS_GN_VARIABLES_H_
 #define TOOLS_GN_VARIABLES_H_
 
 #include <map>
 
 #include "base/strings/string_piece.h"
@@ skipping 125 matching lines @@
 extern const char kDefines_Help[];
 
 extern const char kDepfile[];
 extern const char kDepfile_HelpShort[];
 extern const char kDepfile_Help[];
 
 extern const char kDeps[];
 extern const char kDeps_HelpShort[];
 extern const char kDeps_Help[];
 
-extern const char kForwardDependentConfigsFrom[];
-extern const char kForwardDependentConfigsFrom_HelpShort[];
-extern const char kForwardDependentConfigsFrom_Help[];
-
 extern const char kIncludeDirs[];
 extern const char kIncludeDirs_HelpShort[];
 extern const char kIncludeDirs_Help[];
 
 extern const char kInputs[];
 extern const char kInputs_HelpShort[];
 extern const char kInputs_Help[];
 
 extern const char kLdflags[];
 extern const char kLdflags_HelpShort[];
@@ skipping 72 matching lines @@
 // Note: this is used only for help so this getter is not threadsafe.
 const VariableInfoMap& GetBuiltinVariables();
 
 // Returns the variables used by target generators.
 // Note: this is used only for help so this getter is not threadsafe.
 const VariableInfoMap& GetTargetVariables();
 
 }  // namespace variables
 
 #endif  // TOOLS_GN_VARIABLES_H_