Nodes: StorageArrayElementNode - Remove check for non-existant property.

[cmhhelgeson]

Description

StorageArrayElementNode will query its parent node for it's .instanceIndex property, which doesn't appear to be an existing property or get method.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	685.18 169.62	685.18 169.62	+0 B +0 B
WebGPU	826.02 221.46	825.96 221.44	-66 B -19 B
WebGPU Nodes	825.61 221.36	825.54 221.34	-66 B -19 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	461.96 111.46	461.96 111.46	+0 B +0 B
WebGPU	525.27 141.52	525.27 141.52	+0 B +0 B
WebGPU Nodes	481.93 131.34	481.93 131.34	+0 B +0 B

[cmhhelgeson]

Should node.instanceIndex just be replaced with node.isIndexNode?