Remove old WebSocket implementation from Blink API.

We are deleting the old WebSocket implementation. Since the implementation in
content/ was deleted, we are ready to delete the implementation in the blink
public API layer.

BUG=423201
R=ricea@chromium.org

Review URL: https://codereview.chromium.org/675703004

git-svn-id: svn://svn.chromium.org/blink/trunk@184433 bbb929c8-8fbe-4397-9dbb-9b2b20218538