Remove AIO cache resolver configuration

With the implementation of https://review.openstack.org/322188 the
container cache resolver configurations are no longer used or
necessary.

This patch removes them.

Change-Id: I1b9772bf6b7328f5f033b5035aceac0cdef53d8b

tests/roles/bootstrap-host/tasks/prepare_aio_config.yml

@@ -120,22 +120,6 @@
   tags:
     - generate_secrets
 
-- name: Get the DNS servers in use on the host
-  command: grep nameserver /etc/resolv.conf
-  register: nameservers
-  when:
-    - lxc_cache_resolvers is not defined
-  tags:
-    - get-nameservers
-
-- name: Set lxc_cache_resolvers fact
-  set_fact:
-    lxc_cache_resolvers: "{{ nameservers.stdout_lines }}"
-  when:
-    - lxc_cache_resolvers is not defined
-  tags:
-    - set-fact-lxc_cache_resolvers
-
 - name: Determine if the host has a global pip config file
   stat:
     path: /etc/pip.conf

tests/roles/bootstrap-host/templates/user_variables.aio.yml.j2

@@ -88,10 +88,6 @@ lxc_net_address: 10.255.255.1
 lxc_net_netmask: 255.255.255.0
 lxc_net_dhcp_range: 10.255.255.2,10.255.255.253
 
-## LXC Container Settings
-lxc_cache_resolvers:
-{{ lxc_cache_resolvers | to_nice_yaml }}
-
 ## Security hardening
 apply_security_hardening: true