Remove tests/content/test_document_adoptNode.html.

It is already covered by:

  dom/nodes/Document-adoptNode.html
Remove tests/content/test_document_compatMode.html.

It is already covered by:

  html/dom/documents/resource-metadata-management/document-compatmode-03.html
  dom/nodes/Document-constructor.html
  dom/nodes/DOMImplementation-createHTMLDocument.html
auto merge of #3945 : Ms2ger/servo/rm-tests, r=Manishearth