Remove mpcomplete from OWNERS files

Matt isn't working on chrome stuff anymore

Review URL: https://codereview.chromium.org/1916133002

Cr-Commit-Position: refs/heads/master@{#389860}

chrome/browser/extensions/api/declarative/OWNERS

 battre@chromium.org
-mpcomplete@chromium.org

chrome/browser/extensions/api/declarative_webrequest/OWNERS

 battre@chromium.org
-mpcomplete@chromium.org

chrome/browser/extensions/api/messaging/OWNERS

 # For extension/app messaging.
-mpcomplete@chromium.org
+rdevlin.cronin@chromium.org
+asargent@chromium.org
 
 # For native messaging.
 sergeyu@chromium.org

chrome/browser/extensions/api/omnibox/OWNERS

-# Anyone in the parent directories can review changes to this directory,
-# but the following people are the most knowledgable:
-mpcomplete@chromium.org

chrome/browser/extensions/api/web_request/OWNERS

 battre@chromium.org
-mpcomplete@chromium.org

components/json_schema/OWNERS

 asargent@chromium.org
 calamity@chromium.org
-mpcomplete@chromium.org

content/utility/OWNERS

-mpcomplete@chromium.org
-
 # Mac Sandbox profiles.
 per-file *.sb=set noparent
 per-file *.sb=rsesek@chromium.org

extensions/browser/api/alarms/OWNERS

-mpcomplete@chromium.org