Restore hiding of help buttons in assistant dialogs

Summary:
While there is actually documentation in the manual for such
dialogs, it is only in the KDevelop manual, so anyone else
making use of KDevPlatform would have either wrong or no
matching help popup.
Thus simply restoring kdev4 times code here.

Reviewers: KDevelop, mwolff, kfunk

Reviewed By: KDevelop, mwolff, kfunk

Subscribers: mwolff, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D4068