Remove broken test_getClientRects.html

This broke in ab0d620 and in trying to fix it, it's become clear that I don't
understand the intended behavior of getClientRects().  In fact I only see one
rect in Firefox even when all three <div>s have drawn borders, which confuses
me.  Let's remove the test for now and someone who understands what's going on
(which could be future me!) will re-add it.
auto merge of #1121 : kmcallister/servo/client-rect, r=metajack

This broke in ab0d620 and in trying to fix it, it's become clear that I don't understand the intended behavior of `getClientRects()`.  In fact I only see one rect in Firefox even when all three `<div>`s have drawn borders, which confuses me compared to [the spec](http://www.w3.org/TR/cssom-view/#the-getclientrects-and-getboundingclientrect-methods).  Let's remove the test for now and someone who understands what's going on (which could be future me!) will re-add it.
auto merge of #1125 : Ms2ger/servo/ClientRectList, r=jdm
auto merge of #1126 : Ms2ger/servo/get_scope_and_cx, r=jdm
Make Document a Node.
auto merge of #1079 : jdm/servo/docnode, r=jdm,metajack

The bit I don't like about these changes is that I ended up hiding the document node from the CSS selecting/matching code, so it continues thinking of the document's first child as the root. When I tried to send the full tree including the document node to layout, the layout code refused to create any child flows. When I sent the document's first child without hiding the document, it saw inherited values for properties like font-family, and later tried to treat the document node as an Element when searching for named nodes.
Cleanup DOMParser binding.