extmod/uos_dupterm: Use MP_REGISTER_ROOT_POINTER().

This uses MP_REGISTER_ROOT_POINTER() to register dupterm_objs
instead of using a conditional inside of mp_state_vm_t.

Signed-off-by: David Lechner <david@pybricks.com>

extmod/uos_dupterm.c

@@ -201,4 +201,6 @@ STATIC mp_obj_t mp_uos_dupterm(size_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_uos_dupterm_obj, 1, 2, mp_uos_dupterm);
 
-#endif
+MP_REGISTER_ROOT_POINTER(mp_obj_t dupterm_objs[MICROPY_PY_OS_DUPTERM]);
+
+#endif // MICROPY_PY_OS_DUPTERM

py/mpstate.h

@@ -198,10 +198,6 @@ typedef struct _mp_state_vm_t {
 
     // root pointers for extmod
 
-    #if MICROPY_PY_OS_DUPTERM
-    mp_obj_t dupterm_objs[MICROPY_PY_OS_DUPTERM];
-    #endif
-
     #if MICROPY_PY_LWIP_SLIP
     mp_obj_t lwip_slip_stream;
     #endif