ssl::stream::shutdown and ssl::stream::async_shutdown can never complete with an eof error

[ashtum]

SSL/TLS shutdown operations map the eof error from the underlying protocol layer to a stream_truncated error:
https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/ssl/detail/impl/engine.ipp#L231

When the shutdown procedure completes successfully, eof errors are cleared before calling the completion handler:
https://github.com/chriskohlhoff/asio/blob/master/asio/include/asio/ssl/detail/shutdown_op.hpp#L49

So, there is no need to check and ignore the eof error in shutdown operations:

stream.shutdown(ec);
if (ec == net::error::eof) // Unnecessary
    ec = {};