Remove ServiceIsNullForTesting override for FaviconServiceFactory

Removes ServiceIsNullForTesting override in FaviconServiceFactory
to enable use of FaviconServiceFactory in tests.

BUG=557415

Review URL: https://codereview.chromium.org/1458703009

Cr-Commit-Position: refs/heads/master@{#361108}

ios/chrome/browser/favicon/favicon_service_factory.cc

@@ -57,8 +57,4 @@ scoped_ptr<KeyedService> FaviconServiceFactory::BuildServiceInstanceFor(
           browser_state, ServiceAccessType::EXPLICIT_ACCESS)));
 }
 
-bool FaviconServiceFactory::ServiceIsNULLWhileTesting() const {
-  return true;
-}
-
 }  // namespace ios

ios/chrome/browser/favicon/favicon_service_factory.h

@@ -42,7 +42,6 @@ class FaviconServiceFactory : public BrowserStateKeyedServiceFactory {
   // BrowserStateKeyedServiceFactory implementation.
   scoped_ptr<KeyedService> BuildServiceInstanceFor(
       web::BrowserState* context) const override;
-  bool ServiceIsNULLWhileTesting() const override;
 
   DISALLOW_COPY_AND_ASSIGN(FaviconServiceFactory);
 };