Balancer: remove unnecessary extra argument

Balancer: remove unnecessary extra argument

The full HTML5 spec clones element attributes when they are added to
the ActiveFormattingElements list, so that when an element on that
list is later cloned and reinserted the attributes are the *original*
attributes, not reflecting any changes which embedded JavaScript
in an inline <script> block may have made to them since the element
was pushed.

However, the PHP implementation doesn't run any JavaScript so there's
no way the attributes could change during balancing and there is
thus no reason to keep extra copies of the attributes around.

Change-Id: I89647aeb90c64701d77e862ea9e3d22b19bbdedc