Blacklist nm-tray from System Tools menu category.
Summary: The wise soul who submitted T51 points out that having nm-tray in the menu will likely lead to people clicking on it and littering up their system tray with nm-tray icons, so a blacklist is in order.
Test Plan: Check to see if nm-tray is still in the menu ☺
Reviewed By: tsimonq2
Differential Revision: https://phab.lubuntu.me/D8