Add felt to website_settings OWNERS files

* Adding myself to these OWNERS files as an owner-in-training
* Removing gbillock as he no longer works on the project

BUG=

Review URL: https://codereview.chromium.org/956093002

Cr-Commit-Position: refs/heads/master@{#318129}

chrome/browser/ui/content_settings/OWNERS

 bauerb@chromium.org
 jochen@chromium.org
 markusheintz@chromium.org
+
+# OWNER-in-training
+felt@chromium.org

chrome/browser/ui/website_settings/OWNERS

-gbillock@chromium.org
+# Please use for OWNERS code reviews
 markusheintz@chromium.org
+
+# OWNER-in-training
+felt@chromium.org
+
+# Retired OWNER
+gbillock@chromium.org