Probably moot: Middle-click on QSystemTrayIcon сauses context menu

Summary:
Middle-click on QSystemTrayIcon сauses context menu because inconstant with
http://code.qt.io/cgit/qt/qtbase.git/tree/src/platformsupport/dbustray/qstatusnotifieritemadaptor.cpp?h=5.7#n177
QStatusNotifierItemAdaptor::SecondaryActivate()

BUG: 382855

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: cfeck, davidedmundson, McPain

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D7013

cherry-picked from plasma-integration: b0059b1c8342b5ef95b054a0a5081b5db7e1c7bb
Committed from host : Portia.local