Fix fix/modules/zend.progress-bar.rst broken link

Fix broken links as seen in ```make linkcheck``` output:

>modules/zend.progress-bar.rst:101: [broken] http://livepipe.net/control/progressbar: <urlopen error timed out>
modules/zend.progress-bar.adapter.js-push.rst:101: [broken] http://livepipe.net/control/progressbar: <urlopen error timed out>

Also, LivePipe has been deprecated and is no longer maintained.