Apps: Remove symlinks which are no longer needed

Removed
- drakstats (Seems it was a part of old Mandrake/Mandriva, can't find modern mentions of it)
- file-roller (Gnome provides their own differently-named icon, so this wasn't being used anyway)
- gtklp* (not used, app makes its own xpm-based icons)
- nm-vpn-standalone-lock (removed in nm-applet)
  (https://gitlab.gnome.org/GNOME/network-manager-applet/-/commit/4cf18cc)
- plugin-* (only used for ccsm, and we only provided 5 out of 60+ which looks
            bad/broken/incomplete. better they use their own all-matching icons.)
- system-installer (not used)
- system-software-installer (not used)

Renamed/Updated
- system-software-installer > system-software-install
  system-software-install is the correct freedesktop.org name.
  Resymlinked package icons (rpmdrake, synaptic, update-notifier, yumex > yumex-dnf)
- system-upgrade (deleted duplicate icon from /apps, kept in /actions)