Clean up of docker swarm service (#45525)

* Remove redundant assignation of variable

Found with https://lgtm.com/

* Fix check_mode when force_update is used

lib/ansible/modules/cloud/docker/docker_swarm_service.py

@@ -1069,7 +1069,6 @@ class DockerServiceManager():
             else:
                 changed, changes, need_rebuild, force_update = new_service.compare(current_service)
                 if changed:
-                    changed = True
                     if need_rebuild:
                         if not module.check_mode:
                             self.remove_service(module.params['name'])
@@ -1077,7 +1076,6 @@ class DockerServiceManager():
                                                 new_service)
                         msg = 'Service rebuilt'
                         rebuilt = True
-                        changes = changes
                     else:
                         if not module.check_mode:
                             self.update_service(module.params['name'],
@@ -1085,16 +1083,15 @@ class DockerServiceManager():
                                                 new_service)
                         msg = 'Service updated'
                         rebuilt = False
-                        changes = changes
                 else:
-                    if force_update and not module.check_mode:
-                        self.update_service(module.params['name'],
-                                            current_service,
-                                            new_service)
+                    if force_update:
+                        if not module.check_mode:
+                            self.update_service(module.params['name'],
+                                                current_service,
+                                                new_service)
                         msg = 'Service forcefully updated'
                         rebuilt = False
                         changed = True
-                        changes = changes
                     else:
                         msg = 'Service unchanged'
                 facts = new_service.get_facts()