Don't keep ` 'results.pickle'` in the PythonJob retrieved

[superstar54]

For the moment

In [1]: n = load_node(18919)

In [2]: n.outputs.retrieved.list_object_names()
Out[2]: 
['_error.json',
 '_scheduler-stderr.txt',
 '_scheduler-stdout.txt',
 'aiida.out',
 'results.pickle']

We should not keep it in the retrieved. We should use temporary