[ChromeDriver] Re-enable Java goBack/goForward tests

The following two Java tests no longer appear to be flaky:
PageLoadingTest.testShouldBeAbleToNavigateBackInTheBrowserHistoryInPresenceOfIframes
PageLoadingTest.testShouldBeAbleToNavigateBackInTheBrowserHistory

Bug: chromedriver:653
Change-Id: Iaa0f991a2a3ee785a7505da77e82738622857950
Reviewed-on: https://chromium-review.googlesource.com/1040307
Reviewed-by: Jonathon Kereliuk <kereliuk@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555544}