Remove the unguarded allocation heap.

This isn't really needed and it adds some useless complexity to the block heap manager.

BUG=
R=chrisha@chromium.org

Review URL: https://codereview.appspot.com/138880043

git-svn-id: http://sawbuck.googlecode.com/svn/trunk@2284 15e8cca8-e42c-11de-a347-f34a4f72eb7d