http: revert deprecation of client property

The improper deprecation of the property broke a feature in the
request module used by the bundled npm. This reverts the deprecation
part of this change.

PR-URL: https://github.com/nodejs/io.js/pull/1852
Fixes: https://github.com/nodejs/io.js/issues/1850


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Roman Reiss <me@silverwind.io>