Change mp_obj_type_t.name from const char * to qstr.

Ultimately all static strings should be qstr.  This entry in the type
structure is only used for printing error messages (to tell the type of
the bad argument), and printing objects that don't supply a .print method.

py/objcell.c

@@ -26,7 +26,7 @@ void mp_obj_cell_set(mp_obj_t self_in, mp_obj_t obj) {
 
 const mp_obj_type_t cell_type = {
     { &mp_const_type },
-    "cell",
+    .name = MP_QSTR_, // should never need to print cell type
 };
 
 mp_obj_t mp_obj_new_cell(mp_obj_t obj) {