Hi, @AndyC. I'm not using Panda, but Niara. Anyway, I think the file you are looking for is /themes/panda/order-address.tpl
If it is not, as you know what you are looking for, if you have access to a linux terminal you can go to the themes directory and execute this command:
grep -Hr "auth_right_column"
It will search recursively for the string "auth_right_column" that you want to remove.
Good luck!