don't endorse specific licenses in git.md

since canoeboot is to be gnu fsdg in spirit, and practise,
it must not openly encourage use of the MIT license, no
matter how much i love that license

in practise, most of cbmk is GPL anyway, and the upstream
projects that it uses are also GPL, so this section is
entirely redundant.

remove it.

Signed-off-by: Leah Rowe <info@minifree.org>