Remove Ubuntu Xenial ARM64 base testing

We no longer have any ARM64 Xenial nodes using this, we can remove it.

Change-Id: I20f22a4538bbaa9cb3a3ca11e156c3d02ca5406f

playbooks/roles/base/server/tasks/Ubuntu.xenial.aarch64.yaml

@@ -1,62 +0,0 @@
-# NOTE(ianw) There are ordering issues with this.  Hopefully when
-# we're bionic only we can just remove ntp
-- name: Install ntp
-  package:
-    name: ntp
-    state: present
-
-- name: Ensure NTP service is running
-  service:
-    name: ntp
-    enabled: yes
-    state: started
-
-- name: Install HWE kernel for arm64
-  apt:
-    name: linux-generic-hwe-16.04
-    state: present
-
-# This is copy pasta'd from Debian.yaml because
-#   include_tasks: Debian.yaml
-# Was here previously and resulted in this entire surrounding play
-# stopping/crashing and ansible continued with the next play in the
-# playbook as if nothing were wrong. This is concerning for a couple
-# reasons, why doesnt include_tasks work? and why does it crash ansible
-# without any reported failure.
-- name: Remove packages that make no sense for our servers
-  package:
-    name:
-      - whoopsie
-      - popularity-contest
-      - lxd
-      - lxd-client
-    state: absent
-
-- name: Configure file limits
-  copy:
-    mode: 0644
-    src: debian_limits.conf
-    dest: /etc/security/limits.d/60-nofile-limit.conf
-
-- name: Custom rsyslog config to disable /dev/xconsole noise
-  copy:
-    mode: 0644
-    src: rsyslog.d_50-default.conf
-    dest: /etc/rsyslog.d/50-default.conf
-  notify: Restart rsyslog
-
-- name: Install apt-daily 10periodic file for unattended-upgrades
-  copy:
-     mode: 0444
-     src: 10periodic
-     dest: /etc/apt/apt.conf.d/10periodic
-     owner: root
-     group: root
-
-- name: Install 50unattended-upgrades file for unattended-upgrades
-  copy:
-     mode: 0444
-     src: 50unattended-upgrades
-     dest: /etc/apt/apt.conf.d/50unattended-upgrades
-     owner: root
-     group: root