when deleting an entry, also delete the widgets

previously what would happen is that KCMHotkeys::currentChanged would run, find the new index (-1,-1) now invalid and show the global settings instead. this however left the simple_action's underlying widgets still sitting around referring to the previous index AND holding a dangling trigger point that would eventually crash when the simple_action would be poked by anything

instead force unset the internal state of the simple_action when showing the global settings.

FIXED-IN: 5.23.1 BUG: 443656