Minor performance clean-up in HTML5TreeBuilder

* remove some unnecessary checks

* remove cloning; we don't freeze / share dataAttribs any more

* reorder conditions in isNotPrecededByPre

* use Util.isVoidElement instead of an internal HTML5 list

Change-Id: I7c24c24d6597e3c781d323f76be12d0afb1c0b0c