Remove the hard_dep flag in GN.

tools/gn/target_generator.cc

 // 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.
 
 #include "tools/gn/target_generator.h"
 
 #include "tools/gn/action_target_generator.h"
 #include "tools/gn/binary_target_generator.h"
 #include "tools/gn/build_settings.h"
 #include "tools/gn/config.h"
@@ skipping 190 matching lines @@
     return;
   FillGenericDeps(variables::kDatadeps, &target_->datadeps());
   if (err_->has_error())
     return;
 
   // This is a list of dependent targets to have their configs fowarded, so
   // it goes here rather than in FillConfigs.
   FillForwardDependentConfigs();
   if (err_->has_error())
     return;
-
-  // Mark the "hard_dep" variable as used. This was previously part of GN but
-  // is now unused, and we don't want to throw errors for build files setting
-  // it while the new binary is being pushed.
-  // TODO(brettw) remove this code when all hard_deps are removed.
-  const char kHardDep[] = "hard_dep";
-  if (scope_->IsSetButUnused(kHardDep))
-    scope_->MarkUsed(kHardDep);
 }
 
 void TargetGenerator::FillOutputs() {
   const Value* value = scope_->GetValue(variables::kOutputs, true);
   if (!value)
     return;
 
   Target::FileList outputs;
   if (!ExtractListOfRelativeFiles(scope_->settings()->build_settings(), *value,
                                   scope_->GetSourceDir(), &outputs, err_))
@@ skipping 30 matching lines @@
 
 void TargetGenerator::FillForwardDependentConfigs() {
   const Value* value = scope_->GetValue(
       variables::kForwardDependentConfigsFrom, true);
   if (value) {
     ExtractListOfLabels(*value, scope_->GetSourceDir(),
                         ToolchainLabelForScope(scope_),
                         &target_->forward_dependent_configs(), err_);
   }
 }