puavo-users: remove rest nginx config

is now responsibility of bootserver because this config should also
contain http route for ltsp images.

new config:

`/etc/nginx/site-available/bootserver`
```
server {
       listen 443;
 
       root /usr/share/nginx/www;
 
       location /images {      
              root /opt/ltsp;
              autoindex  on; 
       }        
 
 
       ssl on;
       ssl_certificate /etc/puavo/certs/hostorgcabundle.pem;
       ssl_certificate_key /etc/puavo/certs/host.key;
 
       ssl_protocols SSLv3 TLSv1;
       ssl_ciphers ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv3:+EXP;
       ssl_prefer_server_ciphers on;
 
       location / {
               proxy_pass http://127.0.0.1:9292;
               proxy_set_header HOST $host;
               proxy_set_header X-Real-IP $remote_addr;
               proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
       }
 
       access_log /var/log/nginx/access.log;
       error_log /var/log/nginx/error.log;
}
```