No dedup

Remove the dedup flag, since the `list` command should always deduplicate edges while traversing the graph of our S3 bucket. The bucket must be seen as a graph because concurrent activity can lead to many calls to `s3.List` returning the same paths.

This PR should be reviewed after https://github.com/Shopify/brigade/pull/9, otherwise the change list is long.
r: @shuhaowu , @camilo