Update Entity\MenuItem.php

Remove getter/setter for Children display. (fix. fatal error)
Why are you removing this left join?  Some menus have only children of root, but many have children and grandchildren.  With this join, menus with grandchildren will benefit from only having 1 query to get the entire menu instead of 1 additional query for each child.  This join can be the difference between 1 query and 20 queries for larger menus.