[sddm-theme] Revert bad hack for spacing in action buttons and use a proper…

Authored by filipf on May 21 2019, 5:17 PM.

Description

[sddm-theme] Revert bad hack for spacing in action buttons and use a proper solution

Summary: Merge remote-tracking branch 'origin/Plasma/5.16'

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D21321