[Night Color KCM] Don't show advanced controls for constant mode
Summary:
The user can only change the color temperature when the constant mode is
selected. Therefore, it doesn't make sense to display all irrelevant input
controls (e.g. latitude and longitude inputs, etc).
Test Plan:
Reviewers: Plasma, VDG, GB_2, ngraham
Reviewed By: VDG, GB_2, ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22924