py: Clean up declarations of str type/funcs that are also in unicode.
Background: trying to make an amalgamation of all the code gave some
errors with redefined types and inconsistent use of static.
diff --git a/py/objstrunicode.c b/py/objstrunicode.c
index 63ca6a8..0bb6e04 100644
--- a/py/objstrunicode.c
+++ b/py/objstrunicode.c
@@ -293,7 +293,7 @@
.iternext = str_it_iternext,
};
-mp_obj_t mp_obj_new_str_iterator(mp_obj_t str) {
+STATIC mp_obj_t mp_obj_new_str_iterator(mp_obj_t str) {
mp_obj_str_it_t *o = m_new_obj(mp_obj_str_it_t);
o->base.type = &mp_type_str_it;
o->str = str;