https://macmule.com/2014/12/07/how-to-change-the-automatic-proxy-configuration-url-in-system-preferences-via-a-script/

RemoveAutomaticProxyConfigurationURL.sh

#!/bin/sh
####################################################################################################
#
# License: https://macmule.com/license/
#
####################################################################################################

# Detects all network hardware & creates services for all installed network hardware
/usr/sbin/networksetup -detectnewhardware

IFS=$'\n'

#Loops through the list of network services
for i in $(/usr/sbin/networksetup -listallnetworkservices | tail +2 );
do

    # In absence of being able to unset the auto proxy, set it to " "
    /usr/sbin/networksetup -setautoproxyurl "$i" " "
    echo "Removed proxy for $i"

    # Turn off auto proxy
    /usr/sbin/networksetup -setautoproxystate "$i" off
    echo "Turned off auto proxy for interface $i"

done

unset IFS

echo "Auto proxy for all interfaces turned off"