Revert "libctf: do not corrupt strings across ctf_serialize"

This reverts commit 986e9e3aa0.

(We do not revert the testcase -- it remains valid -- but we are
taking a different, less complex and more robust approach.)

This also deletes the pending refs abstraction without (yet)
replacing it, so some tests will fail for a commit or two.

libctf/ctf-hash.c

@@ -669,12 +669,6 @@ ctf_dynset_lookup (ctf_dynset_t *hp, const void *key)
   return NULL;
 }
 
-size_t
-ctf_dynset_elements (ctf_dynset_t *hp)
-{
-  return htab_elements ((struct htab *) hp);
-}
-
 /* TRUE/FALSE return.  */
 int
 ctf_dynset_exists (ctf_dynset_t *hp, const void *key, const void **orig_key)