Re-License to "MIT OR Aapache-2.0"

The main dependant of `radicle-git`, and its crates, is [`heartwood`].
It is licensed under MIT or Apache-2.0, which has been incompatible with the GPL-3.0 license.
Since the intellectual property of this code base is with the Better Internet Foundation, it was
decided to re-license code in this repository to make the upstream repository compatible.

 - Remove the license headers (and instructions to add them)
 - Add MIT and Apache-2.0 licenses
 - Remove the GPL-3.0 license
 - Change the license declarations in the `Cargo.toml` files

[`heartwood`]: https://app.radicle.xyz/nodes/seed.radicle.xyz/rad:z3gqcJUoA1n9HaHKufZs5FCSGazv5

radicle-git-ext/git-ref-format/macro/src/lib.rs

@@ -1,8 +1,3 @@
-// Copyright © 2021 The Radicle Link Contributors
-//
-// This file is part of radicle-link, distributed under the GPLv3 with Radicle
-// Linking Exception. For full terms see the included LICENSE file.
-
 #[macro_use]
 extern crate proc_macro_error2;