Track deletion timestamp in LinksDeletionUpdate

Track deletion timestamp in LinksDeletionUpdate

Use this to prevent deleting new RC entries at the title of page
deletion that were created since the deletion. This is useful if
an event performs a deletion and makes a new RC entry or if there
is high job queue lag.

Change-Id: I20f6a4aa0a660a24583c1d71f825b73daa748a24