Update git submodules
Update git submodules

* Update plugins/delete-project from branch 'stable-3.1'
  to a1b9777811b9b46bdf1c6258e50fcb629a4be342
  - Merge branch 'stable-3.0' into stable-3.1
    
    * stable-3.0:
      Upgrade bazlets to latest stable-2.16 to build with 2.16.18 API
      Bump Bazel version to 3.1.0
    
    Change-Id: I45cc2fd68ab6a08f51e0325fa1a3087c54ebbd80
    
  - Merge branch 'stable-2.16' into stable-3.0
    
    * stable-2.16:
      Upgrade bazlets to latest stable-2.16 to build with 2.16.18 API
      Bump Bazel version to 3.1.0
    
    Change-Id: I9ce032d0e0fa6437f4594384c5a363bf7cea65c4
    
  - Upgrade bazlets to latest stable-2.16 to build with 2.16.18 API
    
    Change-Id: I6b43af82a92afa58197e4acfedd5c0e96d44246e
    
  - Bump Bazel version to 3.1.0
    
    Change-Id: Ia2518fcbf53ba42bba92667d74b353bc71846319
    
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