Remove dead code from stdenv check-meta license logic

The `unfree` and `unfreeRedistributable` licenses both have `free = false`,
which will trigger the first portion of logic. This removes dead code to
simplify the logic.

As a follow-up, I plan to add an attribute `redistributable = [true|false]`,
which can be used by Hydra to determine whether a given package with a given
license can be included in the channel.