[System Tray] Restore old pin button size
Summary: This size was used before the rewrite (D24720).
Test Plan:
Before:
After:
Reviewers: Plasma, VDG, davidedmundson, broulik
Reviewed By: Plasma, davidedmundson, broulik
Subscribers: davidedmundson, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D25602