Fix tio deleting unix socket file

If tio has a unix file socket open, a second tio instance of tio may
delete the socket file. This change fixes so that it will not be deleted
and tio will instead error and complain about conflicting socket file.

src/socket.c

@@ -77,7 +77,6 @@ void socket_configure(void)
         exit(EXIT_FAILURE);
     }
 
-    unlink(socket_filename());
     if (bind(sockfd, (struct sockaddr *)&sockaddr, sizeof(sockaddr)) < 0)
     {
         error_printf("Failed to bind to socket %s: %s", socket_filename(), strerror(errno));