Remove JS stack info saving code from WebSocketChannel implementations

It was introduced to ensure m_*AtConnection is initialized, but there's
no place where constructor and connect are called separately.

BUG=none

Review URL: https://codereview.chromium.org/94273002

git-svn-id: svn://svn.chromium.org/blink/trunk@162874 bbb929c8-8fbe-4397-9dbb-9b2b20218538