Delete future branch?

[bryevdv]

@mattpap unless you object, I would delete the future branch. We have never really used it and it seems like trying to use it would just be a headache. If the uncommon situation ever does arise, we can just create the appropriate landing branch, if necessary, or else let the PR stay open an extended period.

[mattpap]

future was early stage branch-3.0. There is no need for it anymore and it can be safely deleted.