[EMSUSD-1891] Forced declaration of "inputs:shadow:color" and "inputs:shadow:enable" attributes in all lights

**Describe the bug**
Maya forces the declaration of the "inputs:shadow:color" and "inputs:shadow:enable" attributes in all lights, instead of reverting to fallback.
Just creating a sphereLight in mayaUsd creates those attributes instead of being declared as fallback by the schema. That by itself is an issue but when combined with lights that are under instance prims, a cascade of errors pop up. Even if the light is on a saved separate file, when sublayering it maya automatically tries to declare those attributes.

**Steps to reproduce**
1. Create a SphereLight in Usd
2. Print Layer to Anonymous Layer
3. 2 new attributes are defined

**Expected behavior**
No attribute declaration

**Attachments**

**Specs (if applicable):**
- Windows 11
- Maya 2024.2
- Maya USD 30.0