Remove contrib/mitogen

- the playbook does not work
- the mitogen version is not up to date

This strongly suggests this is not used ; let's drop it.

contrib/mitogen/mitogen.yml

@@ -1,51 +0,0 @@
----
-- name: Check ansible version
-  import_playbook: kubernetes_sigs.kubespray.ansible_version
-
-- name: Install mitogen
-  hosts: localhost
-  strategy: linear
-  vars:
-    mitogen_version: 0.3.2
-    mitogen_url: https://github.com/mitogen-hq/mitogen/archive/refs/tags/v{{ mitogen_version }}.tar.gz
-    ansible_connection: local
-  tasks:
-    - name: Create mitogen plugin dir
-      file:
-        path: "{{ item }}"
-        state: directory
-        mode: "0755"
-      become: false
-      loop:
-        - "{{ playbook_dir }}/plugins/mitogen"
-        - "{{ playbook_dir }}/dist"
-
-    - name: Download mitogen release
-      get_url:
-        url: "{{ mitogen_url }}"
-        dest: "{{ playbook_dir }}/dist/mitogen_{{ mitogen_version }}.tar.gz"
-        validate_certs: true
-        mode: "0644"
-
-    - name: Extract archive
-      unarchive:
-        src: "{{ playbook_dir }}/dist/mitogen_{{ mitogen_version }}.tar.gz"
-        dest: "{{ playbook_dir }}/dist/"
-
-    - name: Copy plugin
-      ansible.posix.synchronize:
-        src: "{{ playbook_dir }}/dist/mitogen-{{ mitogen_version }}/"
-        dest: "{{ playbook_dir }}/plugins/mitogen"
-
-    - name: Add strategy to ansible.cfg
-      community.general.ini_file:
-        path: ansible.cfg
-        mode: "0644"
-        section: "{{ item.section | d('defaults') }}"
-        option: "{{ item.option }}"
-        value: "{{ item.value }}"
-      with_items:
-        - option: strategy
-          value: mitogen_linear
-        - option: strategy_plugins
-          value: plugins/mitogen/ansible_mitogen/plugins/strategy