reqwest: Switch from hyperx to headers
The maintainer of hyperx has kind of special opinions and doesn't want
to play well with the rest of the ecosystem, see
https://github.com/dekellum/hyperx/pull/33 .
This currently causes cargo outdated to fail because of suboptimal
dependencies.
Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/issues/159