Update git submodules
Update git submodules

* Update plugins/replication from branch 'stable-3.1'
  to 6dcaefe343e2c8cd8c9b7eb421cff93d4c226803
  - ReplicateRefUpdate: Drop awkward constructor
    
    A constructor taking an object with a set of refs and also one of those
    refs is an awkward pattern. Remove that code by using a small helper in
    the UriUpdates interface.
    
    Change-Id: I999e57b405d009307bca023e5b9aa7f40c71fb58
    
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