The default behaviour of Ctrl+x is 'Cut|Cutline'. However, if you change it to just 'Cut', it still performs 'Cutline' when no text is selected.
My bindings.json:
{
"Alt-/": "lua:comment.comment",
"CtrlUnderscore": "lua:comment.comment",
"Ctrl-x": "Cut"
}
There seems to be no visible difference between Ctrl-X when running with this bindings.json compared to the default 'Cut|Cutline'. I have verified that this bindings.json is being used in my configuration by making other changes to it.