title: Uninstall protobuf competely
body: <p>Seems brew fails to uninstall protobuf completely:</p>
  
  <pre><code>brew uninstall protobuf --force
  brew uninstall protobuf@3.1 --force
  
  brew info protobuf
  protobuf: stable 3.6.1 (bottled), HEAD
  Protocol buffers (Google's data interchange format)
  https://github.com/protocolbuffers/protobuf/
  Not installed
  From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/protobuf.rb
  ==&gt; Dependencies
  Build: autoconf ✘, automake ✘, libtool ✔
  Recommended: python@2 ✔
  Optional: python ✘
  ==&gt; Options
  --with-python
      Build with python support
  --without-python@2
      Build without python2 support
  --HEAD
      Install HEAD version
  ==&gt; Caveats
  Editor support and examples have been installed to:
    /usr/local/Cellar/protobuf/3.6.1/share/doc/protobuf
  ==&gt; Analytics
  install: 20,550 (30 days), 75,916 (90 days), 307,704 (365 days)
  install_on_request: 10,362 (30 days), 36,197 (90 days), 141,839 (365 days)
  build_error: 0 (30 days)
  
  brew uninstall protobuf
  Error: No such keg: /usr/local/Cellar/protobuf
  
  protoc
  -bash: /usr/local/opt/protobuf@3.1/bin/protoc: No such file or directory
  </code></pre>
  
  <p>What is the proper way to uninstall it completely?</p>