Fix compatibility of LDAP support with Erlang R16A (EJAB-1612)

Fix compatibility of LDAP support with Erlang R16A (EJAB-1612)

As explained in Erlang/OTP git log:
eldap: Remove calls to undocumented asn1rt* functions.
We are about to remove the old asn1rt* modules, so we must remove
the calls that eldap make to them. Since the calls are just a
sanity check, we can just remove the calls. Just doing the decode
will do roughly the same tests and generate similar exceptions.