Update Dart generator to latest version of language spec.

git-svn-id: http://blockly.googlecode.com/svn/trunk@673 c400ca83-b69d-9dd7-9705-49c6b8615e23
Remove Dart from Blockly.

git-svn-id: http://blockly.googlecode.com/svn/trunk@674 c400ca83-b69d-9dd7-9705-49c6b8615e23