[effects/screenshot] Remove outdated reference to KSnapshot
Summary:
Since KSnapshot is no longer used, I modified the text in effect_builtins.cpp to reflect that, changing it to a generic "screenshot tools".
BUG: 408407
FIXED-IN: 5.17.0
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: filipf, davidedmundson, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D21700