Update git submodules
Update git submodules

* Update plugins/singleusergroup from branch 'stable-2.15'
  to 0ffbdf1e5c3daa9d118ee9f53d5c00497cff6454
  - Bazel: Reformat BUILD file with buildifier 0.17.2
    
    Change-Id: I0aac4a7b965b5bce69e8a5370f11d0dda4b27667
    
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