Remove extra s3 hostname

Commit 69802b744811077488714d3d2f7b34985987df98 by @xsleonard  included a change which causes the dreaded response:

    The bucket you are attempting to access must be addressed using the specified endpoint.
    Please send all future requests to this endpoint.

The URL provided, s3-<region-name>.amazonaws.com/<bucket-name>/etc is already sufficient information. Removing the redundant/incorrect host-name fixes this.