Various fixes and simplifications to RefreshLinksJob::runTitle()
* Remove logic for saving slow-to-render parser output. This has
not worked ever since DerivedPageDataUpdater was introduced.
* Make the logic to use cached output actually work. This was
also broken since DerivedPageDataUpdater was added. In order
to pass the output, add a known-revision-output parameter
to both WikiPage::doSecondaryUpdates() and
DerivedPageDataUpdater::prepareUpdate().
* Also factored out some helper methods from runForTitle() in
RefreshLinksJob to make it more readable and avoid the need
for multiple transaction round commit calls. This makes the
case of multiple-title jobs less likely to break again.
* Make use of RefreshLinksJob::runForTitle() return value.
* Add unit tests for multiple-title job case.
Change-Id: I0cd13c424a87653b5a7253c42cd48fe43befd692