Core: Update tested jsdom, drop obsolete workarounds

The latest version supporting Node.js is 3.1.2; some workarounds are not needed
for this version. For example, in jsdom 3.1.2 a document created via
document.implementation.createHTMLDocument( "" ) has a body.

(partially cherry-picked from 95c0a10e15477a5031185e2d656d896905562afa)

Fixes gh-2153
Closes gh-2154

test/unit/data.js

@@ -134,7 +134,7 @@ test("Data is not being set on comment and text nodes", function() {
 });
 
 test("jQuery.acceptData", function() {
-	expect( 11 );
+	expect( 10 );
 
 	var flash, pdf;
 
@@ -142,7 +142,6 @@ test("jQuery.acceptData", function() {
 	ok( jQuery.acceptData( document.documentElement ), "documentElement" );
 	ok( jQuery.acceptData( {} ), "object" );
 	ok( !jQuery.acceptData( document.createElement( "embed" ) ), "embed" );
-	ok( !jQuery.acceptData( document.createElement( "applet" ) ), "applet" );
 
 	flash = document.createElement( "object" );
 	flash.setAttribute( "classid", "clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" );