KF5NewStuff is only used in moleculeview, conditional on Eigen3 and AvogadroLibs

Test Plan: Built fine with AvogadroLibs disabled. Unfortunately no testing if enabled, but should be fine.

Reviewers: KDE Edu, apol

Reviewed By: apol

Subscribers: KDE Edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D9920