Removed hacky hasBadNesting check in DOM fragment unpacking

* The hasBadNesting check in DOM fragment unpacking, while known
  to be hacky, as not worth it since it triggers in situations
  that it shouldn't (nested tables). So, stripped it down to the
  one known case we absolutely will encounter right now and need
  to handle -- nested A-tags because of [[Foo|Bad [[nesting]] here]]
  type of wikitext found in production.

* Fixes RT regression on fr:Rê and pages that use the <hiero>
  extension in infoboxes.

Change-Id: Id55add9096a574681a8ef631d9a71ad745bcd7bd