Remove aiohttp contexts

[tkdrob]

Pull request summary

async with seems to be unnecessary. This PR cleans it up.

Checklist

• [x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
  • [x] I have updated the changelog with a quick recap of my changes.
• [ ] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[aaronhnsy]

afaik, aiohttop context managers are used because the request does not close properly otherwise. In this case you would want to make sure to call ClientResponse.release().

[IAmTomahawkx]

Thanks for the pr, but theres no reason to not use async context managers when they're provided