Revert "Remove pointless data copy in lockscreen delegate"

The switch user greeter accesses it to get the "vtNumber" when you click the "Switch" button.

CHANGELOG: Fixed being unable to switch users from the Switch User screen

This reverts commit cc86474810.

lookandfeel/contents/components/UserDelegate.qml

@@ -28,6 +28,7 @@ Item {
 
     property bool isCurrent: true
 
+    readonly property var m: model
     property string name
     property string userName
     property string avatarPath