LibGL+LibSoftGPU: Remove unused variable `specular_exponent`

This was a duplicate of the `Material::shininess` variable.

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -3104,7 +3104,6 @@ void SoftwareGLContext::sync_light_state()
         material.specular = current_material_state.specular;
         material.emissive = current_material_state.emissive;
         material.shininess = current_material_state.shininess;
-        material.specular_exponent = current_material_state.specular_exponent;
         material.ambient_color_index = current_material_state.ambient_color_index;
         material.diffuse_color_index = current_material_state.diffuse_color_index;
         material.specular_color_index = current_material_state.specular_color_index;

Userland/Libraries/LibSoftGPU/Light/Material.h

@@ -16,7 +16,6 @@ struct Material {
     FloatVector4 specular { 0.0f, 0.0f, 0.0f, 1.0f };
     FloatVector4 emissive { 0.0f, 0.0f, 0.0f, 1.0f };
     float shininess { 0.0f };
-    float specular_exponent { 0.0f };
     float ambient_color_index { 0.0f };
     float diffuse_color_index = { 1.0f };
     float specular_color_index = { 1.0f };