Move ownership of AppSorting from ExtensionPrefs to ExtensionSystem

extensions/browser/null_app_sorting.cc

Index: extensions/browser/null_app_sorting.cc
diff --git a/extensions/browser/null_app_sorting.cc b/extensions/browser/null_app_sorting.cc
index 633bfc7822c558a8a225f0a28f7ce361f1e2a3ee..af4af38927644b6641c6dd32b35f911c204139e3 100644
--- a/extensions/browser/null_app_sorting.cc
+++ b/extensions/browser/null_app_sorting.cc
@@ -23,12 +23,6 @@ NullAppSorting::NullAppSorting() {
 NullAppSorting::~NullAppSorting() {
 }
 
-void NullAppSorting::SetExtensionScopedPrefs(ExtensionScopedPrefs* prefs) {
-}
-
-void NullAppSorting::CheckExtensionScopedPrefs() const {
-}
-
 void NullAppSorting::Initialize(const ExtensionIdList& extension_ids) {
 }