Maya: Collect Look code cleanup + minor bugfix

[BigRoy]

Changelog Description

• Fix: remove from list while iterating over a copy - fixes potential wrong removal from the list of the node types in RENDER_SET_TYPES
• Remove redundant code
  • Remove unused maketx attribute on the class
  • Remove duplicate query of instance_lookup variable.
• Restructure code for readability + improve docstrings

Additional info

Mostly cleanup.

Testing notes:

1. Maya Collect Look should still work
2. Maya Collect Model Render Sets (materials on model publish) should still work for non-shading engines (e.g. object sets)

[LiborBatek]

All working ok when publishing the Look and without any issues. Also added some test maya set with arnold properties...

And when loaded look on the asset:

[mkolar]

@antirotor mergable?

[tokejepsen]

Tested successfully in Maya 2023.