erlcloud_s3:put_object/6 should not count Content-Type in the request headers

Before this change, if the user supplied a Content-Type header for the object, AWS S3 would fail the request signature as below:

> The request signature we calculated does not match the signature you provided. Check your key and signing method.

By removing the option from the HTTPHeaders parameter, the request signing succeeds. The internal `s3_request()` function adds the Content-Type header back later when submitting the request.