Don't advertise on Wayland features that aren't available
Summary:
It's quite stressful and it clearly doesn't push developers to implement the features.
CCBUG: 386271
CCBUG: 377157
Test Plan: Now I don't choose to take a screenshot of the active window and get sad when I can't.
Reviewers: Plasma, mart
Reviewed By: Plasma, mart
Subscribers: hein, ngraham, Spectacle
Tags: Spectacle
Differential Revision: https://phabricator.kde.org/D17082