[WebSocketChannel] Remove logic to delegate ref/deref to subclass

Seems like this code was just copied from some other class. It's not
necessary since all subclasses are just calling RefCounted's default
ref/deref.

BUG=none

Review URL: https://codereview.chromium.org/267593003

git-svn-id: svn://svn.chromium.org/blink/trunk@173070 bbb929c8-8fbe-4397-9dbb-9b2b20218538