We already have a LICENSE file that covers the Zig Standard Library. We
no longer need to remind everyone that the license is MIT in every single
file.
Previously this was introduced to clarify the situation for a fork of
Zig that made Zig's LICENSE file harder to find, and replaced it with
their own license that required annual payments to their company.
However that fork now appears to be dead. So there is no need to
reinforce the copyright notice in every single file.
Start implementing https://github.com/ziglang/zig/issues/4917 which is to rename instream/outstream to reader/writer. This first change allows code to use Writer/writer instead of OutStream/outStream, but still maintains the old outstream names with "Deprecated" comments.
