CorePlugin: Pass context object to lambda connections

Remove some unneeded lambda () brackets.

Change-Id: Id664cfc3b46685f63fb205beaf16a7c271ad95d9
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/designmode.cpp

@@ -56,7 +56,7 @@ static DesignModePrivate *d = nullptr;
 
 DesignMode::DesignMode()
 {
-    ICore::addPreCloseListener([]() -> bool {
+    ICore::addPreCloseListener([] {
         m_instance->currentEditorChanged(nullptr);
         return true;
     });