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/receivecoinsdialog.cpp

@@ -22,7 +22,7 @@
 #include <QTextDocument>
 
 ReceiveCoinsDialog::ReceiveCoinsDialog(const PlatformStyle *_platformStyle, QWidget *parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::ReceiveCoinsDialog),
     columnResizingFixer(nullptr),
     model(nullptr),