/usr/share/gnome/shutdown/libcanberra-logout-sound.sh is in gnome-session-canberra 0.30-0ubuntu3.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 | #!/bin/sh
/usr/bin/canberra-gtk-play --id="desktop-logout" --description="GNOME Logout"
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