Delete an old documentation about [Git.Mem]
Delete an old documentation about [Git.Mem]

It explains hpw to use the /functor/ but it is not really needed and some
details are wrong with the new version of ocaml-git (deletion of [Inflate]/
[Deflate] modules).

mirage/ocaml-git,mirage/ocaml-git,mirage/ocaml-git