Debugger: Call DebuggerItemManager::restoreDebuggers() more directly

Change-Id: I77a293a8754e2aa3dd521e0810006c5f10ae23ff
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/debugger/debuggeritemmanager.h

@@ -22,7 +22,7 @@ public:
     DebuggerItemManager();
     ~DebuggerItemManager();
 
-    void extensionsInitialized();
+    static void restoreDebuggers();
 
     static const QList<DebuggerItem> debuggers();