Remove HttpStreamFactoryJobController's DanglingUntriaged annotations.

Also fix the reasons the annotations were necessary:

HttpStreamFactory was deleting its JobFactory before its
JobControllers, which have a raw pointer to it.

Also, JobControllers can now outlive their
HttpStreamRequest::Delegates, so need to null out that pointer
when it notifies them of its destruction. They were already nulling
out their `request_` at that point, and checking it before trying to
access their delegate, so this didn't lead to issues, apart from
requiring the DanglingUntriaged annotation.

Bug: 40212619
Change-Id: I2431be56934edc6812dab454ec93cdb76b9dba00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402013


Reviewed-by: Adam Rice <ricea@chromium.org>
Commit-Queue: mmenke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279567}