Remove misleading BrowserContextKeyedAPI comment.

extensions/browser/browser_context_keyed_api_factory.h

Index: extensions/browser/browser_context_keyed_api_factory.h
diff --git a/extensions/browser/browser_context_keyed_api_factory.h b/extensions/browser/browser_context_keyed_api_factory.h
index dfd2887a03cd82bd594147b5d6e5fedb52a20c48..fc0add240e066d5b81ea510ee7b1d2e4d44872b4 100644
--- a/extensions/browser/browser_context_keyed_api_factory.h
+++ b/extensions/browser/browser_context_keyed_api_factory.h
@@ -43,9 +43,9 @@ class BrowserContextKeyedAPI : public KeyedService {
   static const bool kServiceIsNULLWhileTesting = false;
 
   // Users of this factory template must define a GetFactoryInstance()
-  // and manage their own instances (typically using LazyInstance or
-  // Singleton), because those cannot be included in more than one
-  // translation unit (and thus cannot be initialized in a header file).
+  // and manage their own instances (using LazyInstance), because those cannot
+  // be included in more than one translation unit (and thus cannot be
+  // initialized in a header file).
   //
   // In the header file, declare GetFactoryInstance(), e.g.:
   //   class HistoryAPI {