Revert "kcms/autostart: Show correct icons for scripts"

This reverts commit bb51b556.

That code uses QFileIconProvider, which uses QGuiApplicationPrivate::platformTheme(), which is null because startplasma(-x11 in my case) only instantiates a QCoreApplication. I do have some old-style startup scripts, so that code was invoked, so the whole session crashed during startup.