service worker: Replace XHR tests with a test in interfaces-sw.https.html

This removes Chromium's xhr-is-not-exposed.html and WPT's xhr.https.html,
replacing them with a simple test in interfaces-sw.https.html.

xhr-is-not-exposed.html was from https://crbug.com/395931
xhr.https.html was from https://bugzilla.mozilla.org/show_bug.cgi?id=931243

Bug: 395931, 688116
Change-Id: I5315bd9e6c0f0fc117ab7924da908a002dda5203
Reviewed-on: https://chromium-review.googlesource.com/755882
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514321}
6 files changed