Revert "Retry updating apt-cache"

This reverts commit 9f5aed800a.

This change was based on an outdated commit.  Since then we stopped
using the apt module and instead use the command module, so the
condition this is looking for is not relevant.

Change-Id: I92f70fdf89c046557a86d26862ae0bdb5a366b99

roles/configure-mirrors/tasks/mirror.yaml

@@ -24,6 +24,3 @@
   become: yes
   command: apt-get update
   when: ansible_os_family == 'Debian'
-  register: apt_cache
-  until: "'cache_updated' in apt_cache"
-  retries: 3