Moved pkg pubspecs to use dev_dependencies where appropriate

BUG=https://code.google.com/p/dart/issues/detail?id=9309

Review URL: https://codereview.chromium.org//12962003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/yaml@20285 260f80e4-7a28-3924-810f-c04153c831b5