Fix shader compilation errors - remove unused legacy functions

Removed leftover functions that were calling non-existent ggxDirectionalAlbedo
and ggxAverageAlbedo. These were legacy from the previous compensation approach
and are not needed with the explicit microsurface scattering implementation.

Fixes:
- Removed ggxEvalWithMultiScatter() stub function
- Removed ggxEnergyCompensation() which called removed functions
- Shader now compiles without errors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: claude

src/shader/bsdf/multiscatter_functions.glsl.js

@@ -128,48 +128,5 @@ vec3 ggxMultiScatterCompensation( vec3 wo, vec3 wi, float roughness, vec3 F0 ) {
 	return vec3( 0.0 );
 }
 
-// Alternative: Single function that returns both single-scatter and multi-scatter
-// This can be more efficient as it reuses calculations
-void ggxEvalWithMultiScatter(
-	vec3 wo,
-	vec3 wi,
-	float roughness,
-	vec3 F0,
-	float D,
-	float G,
-	vec3 F,
-	out vec3 singleScatter,
-	out vec3 multiScatter
-) {
-
-	// Single scatter term (standard Cook-Torrance)
-	float denom = 4.0 * abs( wo.z * wi.z );
-	singleScatter = F * G * D / max( denom, 0.001 );
-
-	// Multi scatter compensation
-	multiScatter = ggxMultiScatterCompensation( wo, wi, roughness, F0 );
-
-}
-
-// Simplified version: Returns just the energy compensation factor
-// Can be used to scale existing single-scatter results
-float ggxEnergyCompensation( float mu, float roughness ) {
-
-	// Returns a factor >= 1.0 that compensates for energy loss
-	// Multiply your existing BRDF by this factor
-
-	vec3 F0 = vec3( 0.04 ); // Assume dielectric for this calculation
-	vec3 E = ggxDirectionalAlbedo( mu, roughness, F0 );
-	float Eavg_scalar = ( E.r + E.g + E.b ) / 3.0;
-
-	float Eavg = ggxAverageAlbedo( roughness );
-
-	// The compensation factor accounts for missing energy
-	// At grazing angles and high roughness, this can be significant
-	float compensation = 1.0 / max( Eavg, 0.001 );
-
-	return compensation;
-
-}
 
 `;