My question is
How do I...delete a xternel refreference(xref), on multiple tabs, at once?

If your xref is inserted in the modelspace, deleting it there will delete it also from all layouts (tabs).

Or if you don't want to delete it, but only to make invisible in all layouts, you can freeze layer which the xref is inserted in or unload (not detach) the xref. If you want to make the xref invisible only in most of layouts, you can use command [CMD]VPLAYER[/CMD] and option freeze -> all and then only in the layout you want to have the xref visible turn the layer on by hand.

Hold shift >click each layout tab >right click at any layout tab> delete..
 
Rman.