Remove NW.js

Given that it's available in the normal repo, we no longer need it here.

https://github.com/caskroom/homebrew-cask/blob/master/Casks/nwjs.rb

Casks/nw-js-32bit.rb

@@ -1,10 +0,0 @@
-cask :v1 => 'nw-js-32bit' do
-  version '0.12.1'
-  sha256 '75b6280b6fb1d068e439a555079de599e57fb59b115a85e0e144e7d86b947d37'
-
-  url "http://dl.nwjs.io/v#{version}nwjs-v#{version}-osx-ia32.zip"
-  homepage 'http://nwjs.io/'
-  license :oss
-
-  stage_only true
-end