Autostart desktop file: a "OnlyShowIn" key must be included

[rapgro]

• desktop-file-validate /home/builder/rpmbuild/BUILDROOT/nm-tray-0.3.0-1.fc27.x86_64/usr/share/applications/nm-tray.desktop /home/builder/rpmbuild/BUILDROOT/nm-tray-0.3.0-1.fc27.x86_64/usr/share/applications/nm-tray.desktop: hint: value "Network;System;Monitor;Qt;TrayIcon" for key "Categories" in group "Desktop Entry" contains more than one main category; application might appear more than once in the application menu /home/builder/rpmbuild/BUILDROOT/nm-tray-0.3.0-1.fc27.x86_64/usr/share/applications/nm-tray.desktop: error: value item "TrayIcon" in key "Categories" in group "Desktop Entry" is a reserved category, so a "OnlyShowIn" key must be included

[palinek]

Removed the TrayIcon in bb62435. (together with 95800b7 it keeps desktop-file-validate quiet)