remove javadoc, dart comments don't use javadoc

This is causing some comments to parse incorrectly, for example, this line of Polymer.dart:

https://github.com/dart-lang/bleeding_edge/blob/258a424a4f915889fa50d557c00820a3c6154ab3/dart/pkg/polymer/lib/polymer.dart#L22

Sublime gets really confused by the `<0` and code is messed up even after the comment, which makes editing hard :). I also see Dart annotations like `@observable` highlighted incorrectly.

Dart documentation comments use a different syntax from javadoc, see: https://www.dartlang.org/articles/doc-comment-guidelines/

@sethladd @timothyarmstrong -- do you mind reviewing?

btw, I wasn't sure about the -JSON.tmLanguage file. I tried to edit it first and use `plutil` to generate the plist file, but it caused other differences. I'm not sure if the 2 files have diverged or if I'm using the wrong command to build that file, so I just manually edited both.