Remove test that fails on WebKit due to bizzare iframe bug

The test verifies that, in an iframe, we can navigate to another page
and then press browser's Back button to restore the previous page.

However, on Chrome and Safari in pjax-disabled mode (browser native
behavior) doing `frame.history.back()` actually goes back in the top
frame, effectively navigating away from the test suite that's running.
There doesn't seem a way to carefully sandbox browser history navigation
to just inside the iframe.

Because this test has the potential to intermittently screw up the whole
test suite run, 🔥 it without mercy as I've already spent countless
hours trying to debug this and have better things to do with my life.

Author: mislav

test/unit/pjax_fallback.js

@@ -99,33 +99,6 @@ asyncTest("sends correct HTTP referer"+s, function() {
   })
 })
 
-asyncTest("adds entry to browser history"+s, function() {
-  var frame = this.frame
-  var count = 0
-
-  frame.onpopstate = function() {
-    window.iframeLoad(frame)
-  }
-
-  this.loaded = function() {
-    count++
-
-    if (count == 1) {
-      equal(frame.location.pathname, "/hello.html")
-      ok(frame.history.length > 1)
-      frame.history.back()
-    } else if (count == 2) {
-      equal(frame.location.pathname, "/home.html")
-      start()
-    }
-  }
-
-  frame.$.pjax({
-    url: "hello.html",
-    container: "#main"
-  })
-})
-
 asyncTest("scrolls to top of the page"+s, function() {
   var frame = this.frame