Remove same-destination checks for view source redirects

Don't require source data hosts for view pings to use strictly the
same destination.

This is generally achievable by embedding multiple pings/attribution
tags on the page.

This both complicates the implementation, and makes changes such as
https://chromium-review.googlesource.com/c/chromium/src/+/3689033
more difficult as it requires persistent attribution state on requests.

This does not contradict with the explainer/spec.

Bug: 1325874
Change-Id: I0cc46ca54753ba523e4c01cb055d5ce4812e5923
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3695617
Reviewed-by: Andrew Paseltiner <apaseltiner@chromium.org>
Commit-Queue: John Delaney <johnidel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1012094}