s3: fix bucket Region auto detection when Region unset in config #2915

Previous to this fix if Region was not set and Endpoint was not set
then we set the endpoint to "https://s3.amazonaws.com/".

This is unecessary because if the Region alone isn't set then we set
it to "us-east-1" which has the same endpoint.

Having the endpoint set breaks the bucket region auto detection with
the error "Failed to update region for bucket: can't set region to
"xxx" as endpoint is set".

This fix removes that check.

backend/s3/s3.go

@@ -1188,9 +1188,6 @@ func s3Connection(opt *Options) (*s3.S3, *session.Session, error) {
 		return nil, nil, errors.New("secret_access_key not found")
 	}
 
-	if opt.Region == "" && opt.Endpoint == "" {
-		opt.Endpoint = "https://s3.amazonaws.com/"
-	}
 	if opt.Region == "" {
 		opt.Region = "us-east-1"
 	}