removing {prod,stage}-log plays, no longer used

The log machines were abandoned long ago.

playbooks/edx-west/prod-log.yml

-- hosts: tag_Name_log10_prod
-  sudo: True
-  vars_files:
-    - "{{ secure_dir }}/vars/users_jumpbox.yml"
-    - "{{ secure_dir }}/vars/datadog_prod.yml"
-  vars:
-    secure_dir: '../../../configuration-secure/ansible'
-    local_dir:  '../../../configuration-secure/ansible/local'
-  roles:
-    - common
-    - datadog

playbooks/edx-west/stage-log.yml

-- hosts: tag_Name_log10_stage
-  sudo: True
-  vars_files:
-    - "{{ secure_dir }}/vars/users_jumpbox.yml"
-  vars:
-    secure_dir: '../../../configuration-secure/ansible'
-    local_dir:  '../../../configuration-secure/ansible/local'
-  roles:
-    - common