Cleanup: Grease Pencil: Remove unused variables.

Previously the change in f5c0c81b7ee6f127f44543179f17fd475f115842 left
an unused variable and is removed by this fix.

source/blender/modifiers/intern/MOD_grease_pencil_thickness.cc

@@ -103,7 +103,6 @@ static void deform_drawing(const ModifierData &md,
 
   MutableSpan<float> radii = drawing.radii_for_write();
   const OffsetIndices points_by_curve = curves.points_by_curve();
-  bke::MutableAttributeAccessor attributes = curves.attributes_for_write();
   const VArray<float> vgroup_weights = modifier::greasepencil::get_influence_vertex_weights(
       curves, mmd.influence);
   const bool is_normalized = (mmd.flag & MOD_GREASE_PENCIL_THICK_NORMALIZE) != 0;