esxcli iscsi adapter discovery statictarget remove -A <vmhba> -a <address> -n <iqn>
"An iSCSI session is active on this vmknic. Either remove this active session or use --force=true to force unbind"
ESXi 6.7
ESXi 7.0
The issue occurs because the boot device may have previously used the iSCSI target.
vmkiscsid -x 'update nodes set "node.boot_target"="No" where "node.name"="<iqn>"'esxcli iscsi adapter discovery statictarget remove -A <vmhba> -a <address> -n <iqn>