Remove SpawnedTestServer::TYPE_HTTP

As of https://chromium-review.googlesource.com/c/chromium/src/+/3452227,
the last use has been removed. SpawnedTestServer is now only used for
WebSockets and proxies.

Bug: 492672
Change-Id: Iff02e13b494a1c34e47bf51d322e72c5d8be404e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3481737
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Steven Valdez <svaldez@chromium.org>
Commit-Queue: Steven Valdez <svaldez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#974207}
NOKEYCHECK=True
GitOrigin-RevId: 1a95aace09e7cb1f333d11af8c5d115a5a39f686