Garbage collect check_defer()

Garbage collect check_defer()

This was a mechanism to ensure that OBJ_cleanup() doesn't remove the
ASN1_OBJECT associated with a custom cipher or digest (that was added
with EVP_add_{cipher,digest}(), while the latter is still referenced
in the OBJ_NAME table.

It had the effect that OBJ_cleanup() wasn't actually called ever from
OPENSSL_cleanup() (it is only called if you load the OID conf module).

Oh, and of course it was once part of the public API. I fixed that two
years ago, almost exactly to the day. Still mentioned in OBJ_create.3.