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/askpassphrasedialog.cpp

@@ -20,7 +20,7 @@
 #include <QPushButton>
 
 AskPassphraseDialog::AskPassphraseDialog(Mode _mode, QWidget *parent, SecureString* passphrase_out) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::AskPassphraseDialog),
     mode(_mode),
     model(nullptr),