Gerrit v3.13 release notes: consolidate changes 499526/499601

Both changes 499526/499601 are associated with the same removal of
support for the label functions, therefore, they do make sense when they
are described together for an easier read by the Gerrit administrator.

Change-Id: I9b49bee781ca59f692753bce416eb88b2c7a8975
1 file changed