Remove left-over PageCache stuff

LayoutTests/fast/events/script-tests/onunload-back-to-page-cache.js

-description('Simulates flow from a page that\'s in the page cache to one that\'s not, and then back to the page cached page.');
-
-onpageshow = function(event) {
-    if (window.name == 'navigated') {
-        testPassed('WebTiming asserts in FrameLoader.cpp did not fire');
-        finishJSTest();
-    } else {
-        if (window.testRunner)
-            testRunner.overridePreference('WebKitUsesPageCachePreferenceKey', 1);
-        setTimeout(function() {location.href = 'data:text/html,<script>onunload=function() {},onload=function(){window.name = \'navigated\';history.back();}<' + '/script>';}, 0);
-    }
-}
-
-var jsTestIsAsync = true;