remove menubar settings

Summary:
global menu automatically enables itself when there is a visualization present
drop the settings kcm altogether
Depends on D9215 and D9216

Test Plan: kcm loads and works correctly without the setting visible anymore

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9267