Update git submodules
Update git submodules

* Update plugins/replication from branch 'stable-3.1'
  to 956fbbc9956aeba435d20267849b00466da48d1b
  - ReplicationTasksStorage: Remove test-only list* methods
    
    Tests should be accurate enough to list from the correct storage areas.
    If tests aren't accurate enough when doing so, then the tests should be
    improved to provide that accuracy.
    
    The updated ReplicationIT and ReplicationFanoutIT tests should be
    investigated in a follow up as tests that currently have an ambiguous
    expected state for tasks. For now, they're worked around by considering
    both running and waiting tasks. As integration tests, these tests
    should be fixed to test behavior, not the specific implementation of
    the storage layer.
    
    Partially reverts Ie164b03579cc917f1095cfde6d77cab630f77759.
    
    Change-Id: I021ad40e35e9f1c9d7076bb6984c864743be829f
    
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