Css: Remove non-functional unit test for negative margin

Thanks @matthewmueller

Closes gh-1474
Ref gh-1918
(cherry picked from commit 30b3b33251abc38386b787c64494265177302b86)

Author: dmethvin

test/unit/css.js

@@ -207,12 +207,9 @@ test( "css() explicit and relative values", 29, function() {
 });
 
 test("css(String, Object)", function() {
-	expect( 20 );
+	expect( 19 );
 	var j, div, display, ret, success;
 
-	jQuery("#nothiddendiv").css("top", "-1em");
-	ok( jQuery("#nothiddendiv").css("top"), -16, "Check negative number in EMs." );
-
 	jQuery("#floatTest").css("float", "left");
 	equal( jQuery("#floatTest").css("float"), "left", "Modified CSS float using \"float\": Assert float is left");
 	jQuery("#floatTest").css("font-size", "20px");