Optimize uninstall tasks a bit

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

roles/custom/matrix-bot-mjolnir/tasks/setup_uninstall.yml

@@ -5,32 +5,21 @@
     path: "{{ devture_systemd_docker_base_systemd_path }}/matrix-bot-mjolnir.service"
   register: matrix_bot_mjolnir_service_stat
 
-- name: Ensure matrix-bot-mjolnir is stopped
-  ansible.builtin.service:
-    name: matrix-bot-mjolnir
-    state: stopped
-    enabled: false
-    daemon_reload: true
-  register: stopping_result
-  when: "matrix_bot_mjolnir_service_stat.stat.exists | bool"
+- when: matrix_bot_mjolnir_service_stat.stat.exists | bool
+  block:
+    - name: Ensure matrix-bot-mjolnir is stopped
+      ansible.builtin.service:
+        name: matrix-bot-mjolnir
+        state: stopped
+        enabled: false
+        daemon_reload: true
 
-- name: Ensure matrix-bot-mjolnir.service doesn't exist
-  ansible.builtin.file:
-    path: "{{ devture_systemd_docker_base_systemd_path }}/matrix-bot-mjolnir.service"
-    state: absent
-  when: "matrix_bot_mjolnir_service_stat.stat.exists | bool"
+    - name: Ensure matrix-bot-mjolnir.service doesn't exist
+      ansible.builtin.file:
+        path: "{{ devture_systemd_docker_base_systemd_path }}/matrix-bot-mjolnir.service"
+        state: absent
 
-- name: Ensure systemd reloaded after matrix-bot-mjolnir.service removal
-  ansible.builtin.service:
-    daemon_reload: true
-  when: "matrix_bot_mjolnir_service_stat.stat.exists | bool"
-
-- name: Ensure matrix-bot-mjolnir paths don't exist
-  ansible.builtin.file:
-    path: "{{ matrix_bot_mjolnir_base_path }}"
-    state: absent
-
-- name: Ensure mjolnir Docker image doesn't exist
-  community.docker.docker_image:
-    name: "{{ matrix_bot_mjolnir_docker_image }}"
-    state: absent
+    - name: Ensure matrix-bot-mjolnir paths don't exist
+      ansible.builtin.file:
+        path: "{{ matrix_bot_mjolnir_base_path }}"
+        state: absent