fastly purge: use reqwest directly because of some library oddness

[syphar]

The error was: https://rust-lang.sentry.io/issues/7060459082/?query=&referrer=issue-stream

Reqwest(reqwest::Error { kind: Request, url: "https://api.fastly.com/service/PqekaQ4n2Cy4QOG85AjuAH/purge", source: hyper_util::client::legacy::Error(SendRequest, hyper::Error(User(DispatchGone), "runtime dropped the dispatch task")) })

Also I built an endless loop, see #3033 ( the fix is also included here).