taskotron: disabling ansible host key checking no longer needed

Tim Flink no longer remembers why he added it (just to dev), but everything
works fine without it.

roles/taskotron/buildslave/tasks/main.yml

@@ -84,10 +84,3 @@
   command: restorecon -R "{{ item.home }}"
   with_items: "{{ slaves }}"
   when: slaves is defined and deployment_type in ['dev', 'stg', 'prod', 'qa-prod', 'qa-stg']
-
-- name: disable ansible host key checking
-  lineinfile:
-    dest: /etc/ansible/ansible.cfg
-    regexp: '^#?host_key_checking = False$'
-    line: 'host_key_checking = False'
-  when: deployment_type in ['dev']