Update curl-exec.xml

[php4fan]

Fixed an error in the description of the return value of curl_exec()

[mmalferov]

It seems to me that there is a reason why this commit has stalled. The constant CURLOPT_FILE is deprecated as of cURL 7.9.7. We should probably use the CURLOPT_WRITEFUNCTION option instead ;-) Therefore, there is no need to mention the CURLOPT_FILE option in the documentation