Remove double adding of MHD_HTTP_HEADER_CONNECTION response header

MHD_create_response_for_upgrade() already adds the MHD_HTTP_HEADER_CONNECTION response header, so
the additional MHD_add_response_header is wrong.

In our application it caused, that on a Apple iPad, the websocket was immediately closed by the
browser(Safari, Chrome, Opera) after the protocol upgrade. Browsers on Linux, Android did not had this issue.

Signed-off-by: Alexander Irion <alexander_irion@mentor.com>

src/examples/websocket_chatserver_example.c

@@ -2241,9 +2241,6 @@ access_handler (void *cls,
        * It requires the value of the Sec-WebSocket-Key header of the request.
        * See also: https://tools.ietf.org/html/rfc6455#section-4.2.2
        */
-      MHD_add_response_header (response,
-                               MHD_HTTP_HEADER_CONNECTION,
-                               "Upgrade");
       MHD_add_response_header (response,
                                MHD_HTTP_HEADER_UPGRADE,
                                "websocket");