Remove Dart Editor Dev Cask

As per the download page
```
Note: As of 1.11, Dart Editor is obsolete and no longer supported. We recommend using DartPad to play with Dart and WebStorm to develop with Dart. For more information, see the announcement.
```

Casks/darteditor-dev.rb

@@ -1,12 +0,0 @@
-cask :v1 => 'darteditor-dev' do
-  version :latest
-  sha256 :no_check
-
-  # googleapis.com is the official download host per the vendor homepage
-  url 'https://storage.googleapis.com/dart-archive/channels/dev/release/latest/editor/darteditor-macos-x64.zip'
-  name 'Dart Editor'
-  homepage 'https://www.dartlang.org/tools/editor/'
-  license :bsd
-
-  app 'dart/DartEditor.app', :target => 'DartEditor-dev.app'
-end