[webapp ssh] remove informational text

[patricklee2]

We should remove those informational text from the console output as they don’t serve any meaningful purpose.

yiliao@yili-ubuntu-03:~$ az webapp ssh -g appsvc_rg_Linux_centralus -n yili-python-up-08
~~Auto-selecting port: 34503~~
~~SSH is available ( username: root, password: Docker! )~~
~~Websocket tracing disabled, use --verbose flag to enable~~
~~Successfully connected to local server..~~
~~Warning: Permanently added '[localhost]:34503' (ECDSA) to the list of known hosts.~~
~~root@localhost's password: ~~
Last login: Wed Jan 16 21:03:58 2019 from 172.20.0.2

  _____                               
  /  _  \ __________ _________   ____  
 /  /_\  \___   /  |  \_  __ \_/ __ \ 
/    |    \/    /|  |  /|  | \/\  ___/ 
\____|__  /_____ \____/ |__|    \___  >
        \/      \/                  \/ 

A P P   S E R V I C E   O N   L I N U X

Documentation: http://aka.ms/webapp-linux

root@ff4d8f60e137:/home/site/wwwroot# less
-bash: less: command not found
root@ff4d8f60e137:/home/site/wwwroot# exit
~~logout~~
~~Connection to localhost closed.~~
~~Client disconnected 1~~
~~Stopped local server.._~~
yiliao@yili-ubuntu-03:~$

[patricklee2]

assign to @patricklee2

[yugangw-msft]

#8324 fixes it