testing/buildbot/OWNERS update.

Add new Chromium committers who understand perf waterfall
to own perf waterfall buildbot configuration file.

Nominate Brian Sheedy as an overall OWNER.

Remove ex-team member from OWNERS.

R=bsheedy@chromium.org, hypan@google.com, wenbinzhang@google.com

Change-Id: I0bfb3c3a86a22f1beeed5eddb561ef37c69c0d17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2099286Reviewed-by: Haiyang Pan <hypan@google.com>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Wenbin Zhang <wenbinzhang@google.com>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749442}

testing/buildbot/OWNERS

@@ -3,13 +3,15 @@
 
 file://infra/OWNERS
 
+bsheedy@chromium.org
 jam@chromium.org
 jochen@chromium.org
 machenbach@chromium.org
 sky@chromium.org
 
 per-file *chromium.perf*.json=crouleau@chromium.org
-per-file chromium.perf.json=simonhatch@chromium.org
+per-file *chromium.perf*.json=wenbinzhang@google.com
+per-file *chromium.perf*.json=hypan@google.com
 per-file chromium.webrtc.json=phoglund@chromium.org
 per-file chromium.webrtc.fyi.json=phoglund@chromium.org