Remove deprecated extension notification from shortcuts_extensions_manager.h/cc

chrome/browser/autocomplete/shortcuts_backend_factory.cc

Index: chrome/browser/autocomplete/shortcuts_backend_factory.cc
diff --git a/chrome/browser/autocomplete/shortcuts_backend_factory.cc b/chrome/browser/autocomplete/shortcuts_backend_factory.cc
index 2fb5a4ba12f935b39ed675266ac0b238c08a8133..36c64cd55aa2b99df18f3d0413c5157fabe9810a 100644
--- a/chrome/browser/autocomplete/shortcuts_backend_factory.cc
+++ b/chrome/browser/autocomplete/shortcuts_backend_factory.cc
@@ -7,7 +7,6 @@
 #include <memory>
 
 #include "base/memory/ptr_util.h"
-#include "chrome/browser/autocomplete/shortcuts_extensions_manager.h"
 #include "chrome/browser/history/history_service_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
@@ -19,11 +18,13 @@
 #include "content/public/browser/browser_thread.h"
 #include "extensions/features/features.h"
 
-namespace {
 #if BUILDFLAG(ENABLE_EXTENSIONS)
+#include "chrome/browser/autocomplete/shortcuts_extensions_manager.h"
+
+namespace {
 const char kShortcutsExtensionsManagerKey[] = "ShortcutsExtensionsManager";
-#endif
 }
+#endif
 
 // static
 scoped_refptr<ShortcutsBackend> ShortcutsBackendFactory::GetForProfile(