Remove fixes for some now not broken request tests (#2165)

Fixes were upstreamed in:

* https://github.com/awslabs/smithy/pull/1040, which was rolled out in
  Smithy v1.18, 10 months ago.
* https://github.com/awslabs/smithy/pull/1392, which was rolled out in
  Smithy v1.26.1, 9 weeks ago.