Remove myself from OWNERS files

I'm no longer actively working on Chromium.

Replace myself with smcgruer@ in most places. Note that
third_party/blink/web_tests is already owned by all committers (*) and
the OWNERS files within are only informative.

Regarding blinkpy, Stephen has made significant contributions there:
https://chromium-review.googlesource.com/q/owner:smcgruer%2540chromium.org+blinkpy+-%2522import+wpt%2522+-%2522roll+wpt%2522
so I'm confident with this nomination.

Change-Id: I38eac7d102ecf86dc9273acde496ca6d9d072c50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2611086Reviewed-by: Rakib Hasan <rmhasan@google.com>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840301}

testing/scripts/OWNERS

@@ -9,9 +9,9 @@ per-file check_static_initializers.py=thakis@chromium.org
 per-file check_static_initializers.py=thomasanderson@chromium.org
 
 per-file run_wpt_tests.py=lpz@chromium.org
-per-file run_wpt_tests.py=robertma@chromium.org
+per-file run_wpt_tests.py=smcgruer@chromium.org
 per-file wpt_common*.py=lpz@chromium.org
-per-file wpt_common*.py=robertma@chromium.org
+per-file wpt_common*.py=smcgruer@chromium.org
 per-file wpt_common*.py=rmhasan@chromium.org
 
 per-file run_performance_tests.py=johnchen@chromium.org

third_party/apache-mac/OWNERS

 davidben@chromium.org
 dpranke@google.com
-robertma@chromium.org

third_party/blink/tools/OWNERS

 dpranke@google.com
 rmhasan@google.com
-robertma@chromium.org
+smcgruer@chromium.org
 tkent@chromium.org
 wangxianzhu@chromium.org
 

third_party/blink/web_tests/external/OWNERS

 # Please do not remove this file. It is needed by blinkpy/w3c/directory_owners_extractor.py
 
 foolip@chromium.org
-robertma@chromium.org
+smcgruer@chromium.org

third_party/blink/web_tests/external/wpt/infrastructure/OWNERS

 foolip@chromium.org
-robertma@chromium.org
 smcgruer@chromium.org

third_party/blink/web_tests/external/wpt/tools/OWNERS

@@ -4,6 +4,6 @@
 # Chromium repo.
 foolip@chromium.org
 lpz@chromium.org
-robertma@chromium.org
+smcgruer@chromium.org
 
 # Team alias: ecosystem-infra@chromium.org