[ModuleInterface] Remove protected helper, redundant with visible dependencyTracker member.

lib/Serialization/SerializedModuleLoader.cpp

@@ -549,8 +549,9 @@ ModuleDecl *SerializedModuleLoaderBase::loadModule(SourceLoc importLoc,
                     isFramework)) {
       return nullptr;
     }
-
-    addDependency(moduleInputBuffer->getBufferIdentifier());
+    if (dependencyTracker)
+      dependencyTracker->addDependency(moduleInputBuffer->getBufferIdentifier(),
+                                       /*isSystem=*/false);
   }
 
   assert(moduleInputBuffer);