remove send_arp_for_ha in nova sample Configuration File

[do3meli]

The sample nova configuration file is most likely inaccurate as it still references send_arp_for_ha and send_arp_for_ha_count which in my opinion has been removed in pike release: https://docs.openstack.org/releasenotes/neutron/pike.html

this needs to be confirmed and if valid should be fixed in the following branches:
* pike
* queens
* rocky
* stein
* master

-----------------------------------
Release: 18.1.1.dev26 on 2019-01-09 02:42
SHA: 380c4bcfab7889e6312eb87d2077277c00cbd0b3
Source: https://git.openstack.org/cgit/openstack/nova/tree/doc/source/configuration/sample-config.rst
URL: https://docs.openstack.org/nova/rocky/configuration/sample-config.html

[Takashi Natsume (natsume-takashi)]

The send_arp_for_ha and send_arp_for_ha_count options are for nova-network, not neutron.
So the sample nova configuration file is accurate.

[Matt Riedemann (mriedem)]

The send_arp_for_ha* options could be deprecated in nova like the other nova-network related config options if that would help avoid confusion.