glsl: remove out of date comment

GLSL 4.40 changed the relevant language in Section 8.13.2 (Interpolation
Functions) to:

   "Component selection operators (e.g., .xy) may be used when specifying
    interpolant."

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30239>

src/compiler/glsl/glsl_to_nir.cpp

@@ -1731,9 +1731,6 @@ nir_visitor::visit(ir_expression *ir)
       ir_dereference *deref = ir->operands[0]->as_dereference();
       ir_swizzle *swizzle = NULL;
       if (!deref) {
-         /* the api does not allow a swizzle here, but the varying packing code
-          * may have pushed one into here.
-          */
          swizzle = ir->operands[0]->as_swizzle();
          assert(swizzle);
          deref = swizzle->val->as_dereference();