dhcp-server: T1707: remove DHCP static-mappings from address pool
Previously when static-mappings have been created the address was still within
the DHCP pool resulting in log entries as follows:
dhcpd: Dynamic and static leases present for 192.0.2.51 dhcpd: Remove host declaration DMZ_PC2 or remove 192.0.2.51 dhcpd: from the dynamic address pool for DMZ
(cherry picked from commit rVYOSONEX6f954ab56768)