The following changes are included:
- Delete per-file license notices at the top of each file.
- Delete the first paragraph of LICENSE-MIT (an inaccurate
pseudo-copyright line), leaving only the text of the MIT license.
Nothing about the license of Serde code has changed, only our
understanding of how to correctly communicate that license has changed.
This mirrors an equivalent change being applied in the rust-lang/rust
repository.
We can continue to publish serde_derive_internals independently but
serde_derive no longer has a dependency on it. This improves compile
time of serde_derive by 7%.
