The system tray example initially was in QtSvg after the Qt 5
modularization split since it depended on it. In the meantime, it
has been moved back to qtbase.
Fixes qdoc warning:
qtbase/src/widgets/util/qsystemtrayicon.cpp:56: warning: Can't link to 'System Tray Icon Example'
Change-Id: Ie3c13baf4ac91ecf0c814885f71ac44dc05b427c
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
