Remove leftover todo related to the dhcpcd support

With commit [1] support for dhcpcd client was added to tempest
but there was not cleaned one of the TODO notes related to that.
So this patch simply cleans that left over.

[1] https://review.opendev.org/c/openstack/tempest/+/871270

Change-Id: I0c94ac5e7fd7b6da0fd051b9ff7d4c226be73f76

tempest/config.py

@@ -1200,7 +1200,6 @@ ScenarioGroup = [
                help='Image container format'),
     cfg.DictOpt('img_properties', help='Glance image properties. '
                 'Use for custom images which require them'),
-    # TODO(yfried): add support for dhcpcd
     cfg.StrOpt('dhcp_client',
                default='udhcpc',
                choices=["udhcpc", "dhclient", "dhcpcd", ""],