Remove NetworkPortalDetector dependency on LoginHandler notifications.

NetworkPortalDetector was not correctly handling the notifications.
There is an ongoing refactor there will likely be some future CLs to
correctly hook up the dependency on proxy auth.

Bug: 1174785, 1371177, http://b/316419561
Change-Id: I9f28e42e8bba63d2d41129b8cadcc229df4890ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5124423
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1238809}