Revert of Cache --whitelisted-extension-id in SimpleFeature.

extensions/common/features/simple_feature.h

Index: extensions/common/features/simple_feature.h
diff --git a/extensions/common/features/simple_feature.h b/extensions/common/features/simple_feature.h
index 5ec95cf91b4a55e2714bcb176e960f4a29cdbe11..9d8c539414bb42f775911dbd76fa7c1cbaed192f 100644
--- a/extensions/common/features/simple_feature.h
+++ b/extensions/common/features/simple_feature.h
@@ -29,18 +29,6 @@
 
 class SimpleFeature : public Feature {
  public:
-  // Used by tests to override the cached --whitelisted-extension-id.
-  class ScopedWhitelistForTest {
-   public:
-    explicit ScopedWhitelistForTest(const std::string& id);
-    ~ScopedWhitelistForTest();
-
-   private:
-    std::string* previous_id_;
-
-    DISALLOW_COPY_AND_ASSIGN(ScopedWhitelistForTest);
-  };
-
   SimpleFeature();
   ~SimpleFeature() override;