Retire some beacon+ping flaky test expectations.

No longer signs of Windows flakiness for these; remove the expectations.

R=mkwst@chromium.org,ojan@chromium.org
BUG=374569
NOTRY=true

Review URL: https://codereview.chromium.org/615053004

git-svn-id: svn://svn.chromium.org/blink/trunk@183036 bbb929c8-8fbe-4397-9dbb-9b2b20218538