Don't leak the world in this new test. (Bug 503832)

--HG--
extra : transplant_source : %14%CB%9Er%1F%93%F6l%F3%11%3Dx%93%97%C3%3D%99%C4%CD%C5

docshell/test/browser/browser_bug503832.js

@@ -26,6 +26,7 @@ function test() {
                 // If titles for fragment URLs aren't set, this code
                 // branch won't be called and the test will timeout,
                 // resulting in a failure
+                historyService.removeObserver(historyObserver, false);
                 finish();
             }
         },