Remove obsolete OS handling in GN.

tools/gn/function_get_target_outputs_unittest.cc

Index: tools/gn/function_get_target_outputs_unittest.cc
diff --git a/tools/gn/function_get_target_outputs_unittest.cc b/tools/gn/function_get_target_outputs_unittest.cc
index cd19d9956663bfc6d1def283e907bbb57cbebed6..c947709a2ed4f7a17d03b12921bd2cbc0820dd22 100644
--- a/tools/gn/function_get_target_outputs_unittest.cc
+++ b/tools/gn/function_get_target_outputs_unittest.cc
@@ -12,8 +12,6 @@ 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_);
   }