Remove net::URLRequest::was_fetched_via_proxy()

There are currently no non-test users of this function.

BUG=653354,940428

Change-Id: Ie48431eea38047971a149c52a35a1cd88c3207c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1545875
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Wojciech Dzier┼╝anowski <wdzierzanowski@opera.com>
Cr-Commit-Position: refs/heads/master@{#645851}
10 files changed