Migrate to upstream `http` crate.

[mkroening]

Some download links to files with non-ASCII filenames have non-ASCII response header values due to faulty encoding (MDL-60697).

Until the issue is resolved upstream, we patch the http crate to not enforce ASCII validation for response header values (9e1e553).

The long-term goal is to migrate back to upstream http, once the issue is resolved in Moodle.