Drop unused variables and lambda captures

Also, add context to connect() expressions where we are or were
capturing "this".

Change-Id: I6e006ba6f83d532478018550d148ee93eca59605
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/debuggerdialogs.cpp

@@ -228,7 +228,7 @@ StartApplicationDialog::StartApplicationDialog(QWidget *parent)
     setWindowTitle(tr("Start Debugger"));
 
     d->kitChooser = new KitChooser(this);
-    d->kitChooser->setKitPredicate([this](const Kit *k) {
+    d->kitChooser->setKitPredicate([](const Kit *k) {
         return !DebuggerKitInformation::configurationErrors(k);
     });
     d->kitChooser->populate();