Merge parser-attr-6321: The NetstringReceiver parser state attributes in t.protocols.basic, deprecated since 10.2, are removed now.

Author: vasuman
Reviewer: thijs
Fixes: #6321


git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@38148 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb