While removing templates, remove the connected elements using about attribute

See http://www.mediawiki.org/wiki/Parsoid/MediaWiki_DOM_spec#Transclusion_content
Template information is stored in parsoid-data attribute with an element with
mw:Transcusion type, while the template rendering can be a different html element.
They are connected using 'about' attribute.

Change-Id: Ie914d53ddd5d902235c4655b1c2ca6116a86df61