Don't set Qt::WindowContextHelpButtonHint on Windows as it basically converts...

Don't set Qt::WindowContextHelpButtonHint on Windows as it basically converts the window in to a dialog

Reviewers: ngraham, mlaurent, dfaure

Reviewed By: ngraham

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D24340