Make chrome/browser/captive_portal/OWNERS direct to net/OWNERS.

This matches what components/captive_portal/OWNERS does.

Bug: None
Change-Id: I59122d9bc35dabc06fecf207f34b683eba6395dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2611045Reviewed-by: Eric Orth <ericorth@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840204}

chrome/browser/captive_portal/OWNERS

-mmenke@chromium.org
+file://net/OWNERS