[dart2js] Remove old unused dart2js tools.

These files haven't been touched in years and, based on my queries, no one is using them.

Bug: #60263
Change-Id: Ie23597bfc9aa624ff63645660aded6c483cfbfc2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/414160
Reviewed-by: Nate Bosch <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs