Remove some TODOs referencing issue 950069.

These TODOs suggest adding tests where the two origins in
NetworkIsolationKey are different to various tests in net/.

It turns out that when the NetworkIsolationKey is usaed as an opaque
key, these cases aren't too interesting.

Bug: 950069
Change-Id: Ie1160b88278503ba81365f86122f04c6de595ec6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545483
Reviewed-by: Shivani Sharma <shivanisha@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828541}