Remove CommandDefinition class In preparation for traits support, remove CommandDefinition class and incorporate the missing functionality into CommandDictionary. BUG: 25841719 Change-Id: Iead48aa0503e9de6061c4c1588b0b930dd82c8d0 Reviewed-on: https://weave-review.googlesource.com/1680 Reviewed-by: Alex Vakulenko <avakulenko@google.com>