Remove UART and improve 399 update (#967)

* Remove UART and improve 399 update

- UART is not officially supported
- change -xvf to -mxvf on 399 update to reduce number of warnings

* UART Linux part recocered

* Communication UART line

---------

Co-authored-by: Julián Caro Linares <jcarolinares@gmail.com>

Author: martab1994

content/hardware/04.pro/boards/portenta-x8/tutorials/01.user-manual/content.md

@@ -940,8 +940,8 @@ Once your Portenta X8 is correctly connected to your PC, launch the following co
 user-pc$: adb shell
 
 portenta-x8$: cd /home/fio
-portenta-x8$: tar -xvf update-latest.tar.gz -C .
-portenta-x8$: tar -xvf aklite-offline-399.tar.gz -C .
+portenta-x8$: tar -mxvf update-latest.tar.gz -C .
+portenta-x8$: tar -mxvf aklite-offline-399.tar.gz -C .
 portenta-x8$: export LD_LIBRARY_PATH=usr/lib/
 portenta-x8$: usr/bin/aklite-offline install --src-dir /var/rootdirs/home/fio/offline-updates/
 ```
@@ -1148,7 +1148,7 @@ Since one of the `I2C` pins is GPIO-multiplexed, you need to detach it from the
     pinMode(PA_12, INPUT);
  }    
  ```
-
+ 
 ### UART
 
 In this case, a Portenta X8 with Portenta Breakout board is used to explore UART communication.
@@ -1157,12 +1157,6 @@ In this case, a Portenta X8 with Portenta Breakout board is used to explore UART
 
 A standard UART is available as `/dev/ttymxc1` in Linux and is mapped to the **`UART1`** port on the Portenta Breakout.
 
-#### UART With Arduino
-
-The `Serial1` object in the Arduino sketch is mapped to the **`UART0`** port on the Portenta Breakout.
-
-Please note that the Arduino RS485 (thus the Arduino Modbus library) library is not supported on the Arduino core of the X8.
-
 ### Bluetooth®
 
 Portenta X8 supports Bluetooth® connectivity just on the Linux side.