I just used awk,tail and head to achieve what you want:

sudo arp-scan --interface=eth0 --localnet| awk '{print $1}'|tail -n +3|head -n -2

this gives the output as

192.168.1.1

192.168.1.3

as I have only these two in my Lan.

Here awk '{print $1}' prints the ip address which is situated in the first column.
tail and head removes unnecessary stuff like the header and just shows the ip addresses.