Replace delegate slots for window shortcut by std::bind expressions
Client had a slot to delay a call when setting up a global shortcut for
the Client. This can be simplified by using a std::bind expression.
Similar the action was connected to a one line lambda which can be
expressed through a std::bind expression as well.
Test Plan: New added auto test still passes
Subscribers: plasma-devel, kwin
Differential Revision: https://phabricator.kde.org/D6801