Expose changed links in LinksUpdate

These links are only really available during the LinksUpdateComplete
hook.

To make sure they are always available this also removes dump links
updates which would prevent this data from being built.

Change-Id: I115f8cf9d3b0a1dba979ceb58b5f14dd0b76ec49
Merge "Expose changed links in LinksUpdate" into wmf/1.22wmf20