clean code related to xpack plugin install

We don't need this anymore as X-Pack is now already included in elasticsearch since 6.3.

tasks/compatibility-variables.yml

@@ -8,9 +8,6 @@
 
 - name: Set the defaults here otherwise they can't be overriden in the same play if the role is called twice
   set_fact:
-    es_open_xpack: true
-    es_install_xpack: false
-    es_users_path: "users"
     es_xpack_conf_subdir: ""
     es_repo_name: "{{ es_major_version }}"
     es_xpack_users_command: "elasticsearch-users"
@@ -19,20 +16,6 @@
     es_other_repo_name: "{{ 'oss-' + es_major_version }}"
     es_other_apt_url: "deb {{ es_repo_base }}/packages/{{ 'oss-' + es_major_version }}/apt stable main"
 
-- name: Detect if es_version is before X-Pack was open and included
-  set_fact:
-    es_open_xpack: false
-  when: "es_version is version_compare('6.3.0', '<')"
-
-- name: If this is an older version we need to install X-Pack as a plugin and use a different users command
-  set_fact:
-    es_install_xpack: true
-    es_xpack_users_command: "x-pack/users"
-    es_xpack_conf_subdir: "/x-pack"
-  when: 
-    - not es_open_xpack
-    - es_enable_xpack
-
 - name: Use the oss repo and package if xpack is not being used
   set_fact:
     es_repo_name: "{{ 'oss-' + es_major_version }}"
@@ -41,5 +24,4 @@
     es_package_name: "elasticsearch-oss"
     es_other_package_name: "elasticsearch"
   when:
-    - es_open_xpack
     - not es_enable_xpack