Replace obj_needs_destructor by more general concept

[tmadlener]

Currently we only generate a destructor for the Obj objects if it is necessary, e.g. here:

podio/python/templates/Obj.h.jinja2

Lines 35 to 39 in 469b739

	{% if obj_needs_destructor %}
	virtual ~{{ obj_type }}();
	{% else %}
	virtual ~{{ obj_type }}() = default;
	{% endif %}

which is populated in the generator, here:

podio/python/podio_class_generator.py

Lines 259 to 260 in 469b739

	needs_destructor = datatype['VectorMembers'] or datatype['OneToManyRelations'] or datatype['OneToOneRelations']
	datatype['obj_needs_destructor'] = needs_destructor

The condition in the generator describes a rather general class of datatypes, i.e. ones that have no relations or vector members. I think the name of obj_needs_destructor should be changed to something that better reflects this more general condition. E.g. is_trivial_type (or something similar).

[soumilbaldota]

We can fix it by changing the variable names to trivial_types instead of needs_destructor

 trivial_types = datatype['VectorMembers'] or datatype['OneToManyRelations'] or datatype['OneToOneRelations']
 datatype['is_trivial_type'] = trivial_types

And is_trivial_type instead of obj_needs_destructor

  {% if is_trivial_type %}
    virtual ~{{ obj_type }}();
  {% else %}
    virtual ~{{ obj_type }}() = default;
  {% endif %}

[soumilbaldota]

I have opened a pull request with the above changes.