Only push the block's parent path onto the stack once during execution

[jasmith-hs]

As I was going to edit some of the logic here for eager execution, I found this redundant logic which pushes and pops the parent path for every node within a block, rather than just doing it once per block.

For instance, if I had a block:

{% block %}
  Hi
  {% if hungry %}
    hungry,
  {% endif %}
  I'm dad!
{% endblock %}

The current logic pushes/pops the parent path for each: Hi, {% if hungry %}, I'm dad!.
Instead, we can just do this once outside the for loop.

The logic was originally added in #363, and there's no need to do it once per node.