net: don't clear all errors on close

Closing a socket clears the error queue of the entire thread, which
seems to be a bit too invasive.

Also I don't find any reason in the PR that added this.

lib/pure/net.nim

@@ -1006,7 +1006,6 @@ proc close*(socket: Socket) =
   try:
     when defineSsl:
       if socket.isSsl and socket.sslHandle != nil:
-        ErrClearError()
         # Don't call SSL_shutdown if the connection has not been fully
         # established, see:
         # https://github.com/openssl/openssl/issues/710#issuecomment-253897666