Remove redundant code in SpdyNetworkTransactionTest setup

Change-Id: Ib2eccbbacda2c843994538f2fe0da470f01cbd3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4060324


Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076462}