Remove a few unused includes from HTMLTreeBuilder
https://bugs.webkit.org/show_bug.cgi?id=106401

Reviewed by Adam Barth.

I happened to notice these while attempting to remove non-thread friendly deps from HTMLTreeBuilder.

No new tests because no new functionality.

* html/parser/HTMLTreeBuilder.cpp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139161 268f45cc-cd09-0410-ab3c-d52691b4dbfc