Revert "When building menu hyerarchies, parent menus to their containers"

This causes crashes in KPart using applications. Like the other reverted
fix, the issue this was trying to solve is handled by
https://codereview.qt-project.org/#/c/195704/

This reverts commit b5af0296cb2f060d9427551e07f470c4d7c39b85.

CCMAIL: montel@kde.org