Don't draw list dividers

Summary:
Depends on D12289

IMHO it looks sleeker without, especially the dividers on top and bottom and before the section headers are disturbing. Since the content of each list item is just one line of text its also not really needed to separate things

Test Plan:
Before:

After:

Reviewers: KDE Connect, VDG, albertvaka

Reviewed By: KDE Connect, albertvaka

Subscribers: kdeconnect, apol, KDE Connect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D12290