tidy: PyTorch now always at 2.x, remove unnecessary code that thinks it can still be 1.x

[danra]

Type of change

Remove code to handle torch version 1.x which can longer have any effect: pyproject.toml requires torch>=2.6

Checklist:

• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• I have not rewritten tests relating to key interfaces which would affect backward compatibility