Connection::isSecure method is untrusted

[AmraniCh]

Description

Since the PHP FTP extension provides only an explicit FTP over SSL/TLS connections (ftp_ssl_connect), we cannot determine if a successful connection is handled secured or not, therefore the ConnectionInterface::isSecure method is untrusted and shouldn't depend on it.

Suggestion

Deprecating of ConnectionInterface::isSecure and remove it from future releases.