curl_multi_info_read.3: fix example formatting

At this point, there are no other \fBmsg\fP types defined.

.SH EXAMPLE

.nf

struct CURLMsg *m;

/* call curl_multi_perform or curl_multi_socket_action first, then loop

    curl_easy_cleanup(e);

  }

} while(m);

.fi

.SH "RETURN VALUE"

A pointer to a filled-in struct, or NULL if it failed or ran out of

structs. It also writes the number of messages left in the queue (after this