Remove unsupported attributes from QGraphicsWidgets

Summary:
Qt::WA_InputMethodEnabled and WA_StaticContents attributes
are only supported by QWidget, not QGraphicsWidget.
Resulted warnings like
"QGraphicsWidget::setAttribute: unsupported attribute 14".

Don't think this has ever worked as intended.

Reviewers: boemann

Subscribers: Calligra-Devel-list

Tags: #calligra:_3.0

Differential Revision: https://phabricator.kde.org/D19759