revert: hyper v1 upgrade (for now)

[seanmonstar]

It seems a few things make it so this different strategy would be better: revert the breaking changes from master for now, and keep them in a 0.12-dev branch.

• 0.11.25 broke the MSRV on macOS.
• The breaking changes aren't fully ready for 0.12 to go out, and I prefer keeping master ready to release with each commit.

I don't mean this as a de-prioritization. This just reflect reality and makes things easier to move forward. Breaking changes will still be worked on and merged into 0.12-dev. As soon as they're all complete, we can rebase onto master and ideally release the same day (or next day).

[ArcticLampyrid]

Sorry to trouble you. The hot day just makes me be irascible.

I'm curious if there's a roadmap in place for the release of a new version of reqwest, incorporating Hyper v1. While I understand that this presents an opportunity for making breaking changes to reqwest, the slow progress could potentially hinder the upgrade process for many packages. I've noticed numerous pull requests being delayed due to this factor.