Removed extra "Upgrade" token in Connection reply header in tests and examples

MHD automatically adds "Upgrade" header, no need to add it for the
second time.

doc/examples/websocket.c

@@ -382,9 +382,6 @@ access_handler (void *cls,
       /* upgrade the connection */
       response = MHD_create_response_for_upgrade (&upgrade_handler,
                                                   NULL);
-      MHD_add_response_header (response,
-                               MHD_HTTP_HEADER_CONNECTION,
-                               "Upgrade");
       MHD_add_response_header (response,
                                MHD_HTTP_HEADER_UPGRADE,
                                "websocket");

src/microhttpd_ws/test_websocket_browser.c

@@ -494,9 +494,6 @@ access_handler (void *cls,
       /* upgrade the connection */
       response = MHD_create_response_for_upgrade (&upgrade_handler,
                                                   NULL);
-      MHD_add_response_header (response,
-                               MHD_HTTP_HEADER_CONNECTION,
-                               "Upgrade");
       MHD_add_response_header (response,
                                MHD_HTTP_HEADER_UPGRADE,
                                "websocket");