Remove obsolete OS handling in GN.

tools/gn/function_get_target_outputs_unittest.cc

 // 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.
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/target.h"
 #include "tools/gn/test_with_scope.h"
 
 namespace {
 
 class GetTargetOutputsTest : public testing::Test {
  public:
   GetTargetOutputsTest() {
-    // Want consistent target names so explicitly set platform.
-    setup_.settings()->set_target_os(Settings::LINUX);
     setup_.scope()->set_item_collector(&items_);
   }
 
   Value GetTargetOutputs(const std::string& name, Err* err) {
     FunctionCallNode function;
     std::vector<Value> args;
     args.push_back(Value(nullptr, name));
     return functions::RunGetTargetOutputs(setup_.scope(), &function, args, err);
   }
 
@@ skipping 70 matching lines @@
       "//out/Debug/{{source_file_part}}.two");
 
   items_.push_back(action);
 
   Err err;
   Value result = GetTargetOutputs("//foo:bar", &err);
   ASSERT_FALSE(err.has_error());
   AssertTwoStringsEqual(result, "//out/Debug/file.txt.one",
                         "//out/Debug/file.txt.two");
 }