Revert "change ImageServingHelper::onLinksUpdateComplete to use the image list as provided by LinksUpdate, rather than building up the list of images itself."

This reverts commit 703b0d3ec65e784131380fcb474066bc7aa0e1f5.
removing unused call
Merge pull request #2250 from Wikia/BAC-1107

reverting changes for ImageServing index generation