Stop deflate-stream support.

Buffer draining code that was required to close deflate-stream enabled
session cleanly will be also removed.
Review URL: https://codereview.appspot.com/8358043

git-svn-id: http://pywebsocket.googlecode.com/svn/trunk@744 4ff78f4a-9131-11de-b045-6380ec9940d4