LanguageClient: fix memory leak

When removing actions from a widget the action is not magically deleted,
so manually delete the language client toolbar action of the editor
after the last client was shutdown.

Change-Id: I6a5a079d4a44724f92d291040925df73f7eb747b
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/languageclient/languageclientutils.cpp

@@ -213,6 +213,7 @@ void updateEditorToolBar(Core::IEditor *editor)
         } else {
             widget->toolBar()->removeAction(action);
             actions.remove(widget);
+            delete action;
         }
     } else if (client) {
         const QIcon icon = Utils::Icon({{":/languageclient/images/languageclient.png",