Revert "[DevTools] HAR: add "connection" field."

This reverts r156364. I believe this broke
inspector-protocol/runtime-getProperties.html on Mac.

TBR=eustas@chromium.org
BUG=276262

Review URL: https://codereview.chromium.org/22968006

git-svn-id: svn://svn.chromium.org/blink/trunk@156386 bbb929c8-8fbe-4397-9dbb-9b2b20218538