Globally disable WindowContextHelpButtonHint

Do set the global application flag AA_DisableWindowContextHelpButton
to avoid having to unset the default WindowContextHelpButtonHint
in every single dialog.

AA_DisableWindowContextHelpButton was added in Qt 5.10.

Change-Id: I21fe8bc5ddfa4c01ec7a799b04bfb6ff1c9d6d86
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/plugindialog.cpp

@@ -55,8 +55,6 @@ PluginDialog::PluginDialog(QWidget *parent)
     : QDialog(parent),
       m_view(new ExtensionSystem::PluginView(this))
 {
-    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
-
     auto vl = new QVBoxLayout(this);
 
     auto filterLayout = new QHBoxLayout;