Remove "Generated output with Corollary" from each file

[tcr]

Files are now modified by hand, so this is no longer true!

[birkenfeld]

While at it, do you want to add some sort of copyright/license header?

[birkenfeld]

Ping re. license. There also isn't a toplevel LICENSE file, but Cargo.toml indicates the standard MIT/Apache license.

(Can we take parts from language-c, which is BSD-3-Clause, and put them into parser-c under MIT/Apache?)