Minor net/http unit test cleanup

Minor cleanup that I came across

 #cleanup

Bug: None
Change-Id: Ib2d3ae596f92b1f22b667b24f189fcc359b00403
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5601172


Commit-Queue: Andrew Williams <awillia@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313168}