basic/hashmap,set: inline trivial set_iterate() wrapper

The compiler would do this to, esp. with LTO, but we can short-circuit the
whole process and make everything a bit simpler by avoiding the separate
definition.

(It would be nice to do the same for _set_new(), _set_ensure_allocated()
and other similar functions which are one-line trivial wrappers too. Unfortunately
that would require enum HashmapType to be made public, which we don't want
to do.)

src/basic/hashmap.c

@@ -730,10 +730,6 @@ bool _hashmap_iterate(HashmapBase *h, Iterator *i, void **value, const void **ke
         return true;
 }
 
-bool set_iterate(const Set *s, Iterator *i, void **value) {
-        return _hashmap_iterate(HASHMAP_BASE((Set*) s), i, value, NULL);
-}
-
 #define HASHMAP_FOREACH_IDX(idx, h, i) \
         for ((i) = ITERATOR_FIRST, (idx) = hashmap_iterate_entry((h), &(i)); \
              (idx != IDX_NIL); \