Eliminate ash/system/network/vpn_util.cc

These utility functions are now only used in one file and can be
moved there.

Bug: 862420
Change-Id: I747ad7d8180bf6b7c85b88c7d401a38837838320
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1612560
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661401}
4 files changed