Remove unnecessary sync in line input mode

This caused a problem for some highly timing sensitive modem read-eval-print
loops because the input line and line termination characters (cr/nl) would be
shifted out on the UART with too big delay inbetween because of two
syncs.

src/tty.c

@@ -2669,7 +2669,6 @@ int tty_connect(void)
                                         // Write current line to tty device
                                         char *rl_line = readline_get();
                                         tty_write(device_fd, rl_line, strlen(rl_line));
-                                        tty_sync(device_fd);
                                     }
                                     else
                                     {