scripted-diff: Remove unused "What's This" button in dialogs on Windows

-BEGIN VERIFY SCRIPT-
git grep -l 'QDialog(parent)' -- src/qt | xargs sed -i -E 's/QDialog\(parent\)/QDialog\(parent, GUIUtil::dialog_flags\)/g'
-END VERIFY SCRIPT-

src/qt/intro.cpp

@@ -119,7 +119,7 @@ int GetPruneTargetGB()
 } // namespace
 
 Intro::Intro(QWidget *parent, int64_t blockchain_size_gb, int64_t chain_state_size_gb) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::Intro),
     thread(nullptr),
     signalled(false),