Revert "TrayIcon: Explicitly show/hide the main window if requested"
This was fixed in KNotification 5.44.
Other KDE Applications already depend on 5.47 in 18.08, so this workaround
will definitely be unnecessary by the time 18.12 is released.
This reverts commit ccefe1842cb34a530fa18cd878b7a7f56654d99c.