sudo: T6926: remove spam messages to syslog

Right now every command that's executed via op-mode/conf-mode is logged with a
session entry/exit and command execution into syslog.

sudo[1082396]: vyos : TTY=pts/1 ; PWD=/home/vyos ; USER=root ; COMMAND=/usr/bin/mv /tmp/config.boot.1082388 /opt/vyatta/etc/config/archive/config.boot
sudo[1082396]: pam_unix(sudo:session): session opened for user root(uid=0) by vyos(uid=1002)
sudo[1082396]: pam_unix(sudo:session): session closed for user root
sudo[1082399]: vyos : TTY=pts/1 ; PWD=/home/vyos ; USER=root ; COMMAND=/usr/sbin/logrotate -f -s /opt/vyatta/etc/config/archive/lr.state /opt/vyatta/etc/config/archive/lr.conf
sudo[1082399]: pam_unix(sudo:session): session opened for user root(uid=0) by vyos(uid=1002)
sudo[1082399]: pam_unix(sudo:session): session closed for user root

This heavily bloats remote logging services - remove the log entries