[Protected Audience] Stop disabling a feature in browser tests.

In particular, stop disabling
LocalNetworkAccessAllowPotentiallyTrustworthySameOrigin, so it can
be removed.

The InterestGroupPrivateNetworkBrowserTests expected updates to fail
when the updateURL was on a private IP, and an update was
triggered by a page on a public IP. The flag was needed to ensure
the requests failed. However, the new private network access behavior
is to allow same-origin requests, even when making public
network-initiated calls to private networks. Since updateURLs are same-
origin to the owner, which is used as the initiator, that means
when the feature enabled, update requests cannot fail due to
private networking requests.

This is pretty analogous to a cached main frame URL from a public
network making a same-origin request on a private network later, when
retrieving the network from the cache, so it makes sense the behavior
is the same.

This CL modifies the browser tests so that they now expect the
update requests to succeed. They also test that the correct
IPAddressSpace is used for the requests. Plumbing it through
correctly currently has no observable effect, other than in the
values sent to the network service, but it will matter if the
same-origin exemption logic is ever removed.

Bug: 356624834
Change-Id: Ie241e2bc2a2ff62c02c948759cec0319a591f9f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6108176
Reviewed-by: Caleb Raitto <caraitto@chromium.org>
Commit-Queue: mmenke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1399437}