Modify c/b/c/apps/intent_helper/OWNERS for better non-PST coverage

BUG=None
TEST=no code change

Change-Id: I29b509c01415dcbce90e129ce168b35e771b7a25
Reviewed-on: https://chromium-review.googlesource.com/994172Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547941}

chrome/browser/chromeos/apps/intent_helper/OWNERS

-# For ARC++ related code
+# For ARC related code
 djacobo@chromium.org
-yusukes@chromium.org
+# For ARC related code, backup reviewers
+file://chrome/browser/chromeos/arc/OWNERS