Unify cryptotoken OWNERS.

The API implementations and the code that uses that API generally evolve
together so it makes sense to have the same owners for each. Also arnarb
has lost commit privileges and juanlang is away, so this code is
otherwise stuck.

Bug: none
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Iadc44d9cf12c975f5857a1601fe88b3e09e16c9b
Reviewed-on: https://chromium-review.googlesource.com/804405Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Commit-Queue: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521169}

chrome/browser/extensions/api/cryptotoken_private/OWNERS

 agl@chromium.org
+mab@chromium.org
 kpaulhamus@chromium.org
 arnarb@chromium.org
+juanlang@chromium.org

chrome/browser/resources/cryptotoken/OWNERS

-arnarb@chromium.org
-juanlang@chromium.org
+file://chrome/browser/extensions/api/cryptotoken_private/OWNERS