The "Navigation" Block is not a widget, it is a sideNAV block that is part of an action in a controller (and has behaviors based on if its on AMS Index or AMS Category pages). This block is actual template code as part of the xa_ams_index template as well as the xa_ams_category_view template. The Navigation block can easily be removed or commented out tho (simple template edits).
AMS does include a Widget Definition that allows you to create category navigation widgets, which was originally designed for use outside of AMS, like on Forum Home for example and for Modular Index, but can also be used on AMS sidenav and sidebar positions (altho, the behavior of category widget is NOT the same as the behavior of the more complex Navigation sidenav block, especially on Category Pages).
Hit me up in Conversation so I can walk you through removing the Navigation block(s) from specific pages