/usr/share/live/images/gnome-desktop/config/bootloaders/syslinux/syslinux.cfg is in open-infrastructure-system-images 20161101-lts2-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | include menu.cfg
default vesamenu.c32
prompt 0
timeout 0
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