Fix the flaky Warmup URL test in data reduction proxy

components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
index 3434816604704f457323178e0599d8e8013b6276..5bc7b57a8b9b61214535559f351d462ebba180d4 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.h
@@ -228,10 +228,6 @@ class DataReductionProxyConfig
   // Updates the Data Reduction Proxy configurator with the current config.
   void UpdateConfigForTesting(bool enabled, bool restricted);
 
-  // Updates the callback that is called when the warmup URL has been fetched.
-  void SetWarmupURLFetcherCallbackForTesting(
-      base::Callback<void()> warmup_url_fetched_callback);
-
  private:
   friend class MockDataReductionProxyConfig;
   friend class TestDataReductionProxyConfig;