Remove eugenebut from ios/chrome/browser/webui owners

Bug: None
Change-Id: I5a6f5afaf8892abb49b59dc15dbfa4c29b6a31f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633847
Auto-Submit: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844427}

ios/chrome/browser/webui/OWNERS

-eugenebut@chromium.org
 michaeldo@chromium.org