No need to force https (olivere#1326)

There is no need to force https in the aws signer.
This already happens by default, and forcing it ruins the ability to test in dev against an Elasticsearch docker container.

Close olivere#1328

aws/v4/aws_v4.go

@@ -49,7 +49,6 @@ func (st Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 		return st.client.Do(req)
 	}
 
-	req.URL.Scheme = "https"
 	if strings.Contains(req.URL.RawPath, "%2C") {
 		// Escaping path
 		req.URL.RawPath = url.PathEscape(req.URL.RawPath)