py: Remove mp_load_const_str and replace uses with inlined version.
diff --git a/py/vm.c b/py/vm.c
index d6ff153..3423e9e 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -213,7 +213,7 @@
 
                 ENTRY(MP_BC_LOAD_CONST_STRING): {
                     DECODE_QSTR;
-                    PUSH(mp_load_const_str(qst));
+                    PUSH(MP_OBJ_NEW_QSTR(qst));
                     DISPATCH();
                 }