Comment 0 for bug 1508189

dhcp/router_delete_namespaces[1] options have been defined as a workaround to an iproute2 limitation[1] corrected 2 years ago.

That's why it's to remove them after their deprecation in Liberty.

[1] https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?id=58a3e8270fe72f8ed92687d3a3132c2a708582dd