Remove old task retry mechanism

Closes #1710 (closed)

Prevents a user to update a task to pending state.

arkindex/ponos/serializers.py

@@ -183,14 +183,14 @@ class TaskTinySerializer(TaskSerializer):
 
     def validate_state(self, state):
         """
-        Only allow a user to manually stop or retry a task
+        Only allow a user to manually stop a task
         """
-        allowed_transitions = {
-            state: [State.Pending] for state in FINAL_STATES
-        }
-        allowed_transitions.update({State.Running: [State.Stopping]})
-        if self.instance and state not in allowed_transitions.get(self.instance.state, []):
-            raise ValidationError(f"Transition from state {self.instance.state} to state {state} is forbidden.")
+        if (
+            self.instance
+            and self.instance.state != state
+            and (self.instance.state != State.Running or state != State.Stopping)
+        ):
+            raise ValidationError("State can only be updated from running to stopping")
         return state
 
     def update(self, instance: Task, validated_data) -> Task: