Destroy device bound SessionService in ~URLRequestContext

While https://crrev.com/c/6824767 removes the risk of a UAF, we still
trigger the assert because we don't destroy the SessionService until
after the assert occurs.

Bug: 435868897
Change-Id: Id773859779e022a2d5a84a62da3f3f098e2c66e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6825797
Reviewed-by: Nick Harper <nharper@chromium.org>
Reviewed-by: thefrog <thefrog@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1498369}