x11-toolkits/kf5-kxmlgui: remove unnecessary dependencies

attica5 was dropped upstream in [1], textwidgets in [2], and
windowsystem in [3].

[1] https://invent.kde.org/frameworks/kxmlgui/-/commit/cca89e765841d1a9e43f9a28ec94c116f1ab1d05
[2] https://invent.kde.org/frameworks/kxmlgui/-/commit/13cb497277fa06d1a25426ddde04ad48c92d2da5
[3] https://invent.kde.org/frameworks/kxmlgui/-/commit/ffd68935c2ef48fc60cbbb1b4159d49a018e597b