Revert "Workaround to prevent an ambigous remove shortcut"

This reverts commit b4155da24fbb4c9813faa90a4c35b3a763397e78.
Fix adding ambigous shortcuts from submenus

A context menu action can contain a menu containing further actions, whose
shortcuts haven't been checked for ambiguity before.

This fixes shortcuts like <Del> for removing single contacts.