How to change grub boot menu on a (formerly) live linux system?

So I converted a usb live linux install (Tails) from USB to virtualbox using VBoxManage convertfromraw. For it to boot in virtualbox, I need to remove one thing from the boot commandline (live-media=removable). This option is not in the usual /etc/default/grub or grub.d locations. I did find it in: /lib/live/mount/medium/syslinux/live.cfg. I'm not sure how that ends up in the grub commandline. In fact, there is nothing in /boot/grub except unicode.pf2, so I think there is some other mechanism going on here. This is EFI, also. I'm reluctant to run update-grub in case this command line is being put together in a different manner.