Remove some MISSING expectations as the underlying issue has been fixed.

This patch also removes some commented-out lines in TestExpectations which
do not seem worth keeping.

BUG=390732
TBR=junov@chromium.org,eae@chromium.org

Review URL: https://codereview.chromium.org/374293002

git-svn-id: svn://svn.chromium.org/blink/trunk@177705 bbb929c8-8fbe-4397-9dbb-9b2b20218538