QmlEditor: Remove QtQuick->Preview from tools menu

This only works when a qmlviewer is in the PATH, which is non obvious.
Removing the feature therefore completely.

src/plugins/qmljseditor/qmljseditorconstants.h

@@ -36,7 +36,6 @@ namespace QmlJSEditor {
 namespace Constants {
 
 // menus
-const char * const M_QTQUICK = "QtQuickDesigner.Menu";
 const char * const M_CONTEXT = "QML JS Editor.ContextMenu";
 
 const char * const RUN_SEP = "QmlJSEditor.Run.Separator";