Line2NodeMaterial: Remove unused `lineWidth` property. (#31401)

* Update Line2NodeMaterial.js

In the global environment of three.js, the `lineWidth` in `Line2NodeMaterial` does not take effect and is essentially ineffective. To modify the line width, it is necessary to use the `linewidth` setting. Additionally, neither `Material` nor `NodeMaterial` contains a `linewidth` property. Therefore, the `lineWidth` property in `Line2NodeMaterial` should be changed to `linewidth`, and its default value should be set to 1.

* Update Line2NodeMaterial.js

delete `linewidth` property.

src/materials/nodes/Line2NodeMaterial.js

@@ -66,14 +66,6 @@ class Line2NodeMaterial extends NodeMaterial {
 		 */
 		this.dashOffset = 0;
 
-		/**
-		 * The line width.
-		 *
-		 * @type {number}
-		 * @default 0
-		 */
-		this.lineWidth = 1;
-
 		/**
 		 * Defines the lines color.
 		 *