aco: remove aco::rt_stack variable

Since we initialize scratch in the RT proglog,
there is no need for this variable anymore.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21780>

src/amd/compiler/aco_instruction_selection.cpp

@@ -8934,7 +8934,6 @@ visit_intrinsic(isel_context* ctx, nir_intrinsic_instr* instr)
    case nir_intrinsic_load_rt_dynamic_callable_stack_base_amd:
       bld.copy(Definition(get_ssa_temp(ctx, &instr->dest.ssa)),
                get_arg(ctx, ctx->args->rt_dynamic_callable_stack_base));
-      ctx->program->rt_stack = true;
       break;
    case nir_intrinsic_overwrite_vs_arguments_amd: {
       ctx->arg_temps[ctx->args->vertex_id.arg_index] = get_ssa_temp(ctx, instr->src[0].ssa);