Fix GSS krb5 acceptor acquire_cred error handling

When acquiring acceptor creds with a specified name, if we fail to
open a replay cache, we leak the keytab handle.  If there is no
specified name and we discover that there is no content in the keytab,
we leak the keytab handle and return the wrong major code.  Memory
leak reported by Andrea Campi.

ticket: 7805
target_version: 1.12.1
tags: pullup
Don't require krb5.conf without KRB5_DNS_LOOKUP

For a long time we have allowed krb5 contexts to be initialized in the
absence of krb5.conf--but only if KRB5_DNS_LOOKUP is defined,
presumably on the theory that no KDCs could be contacted without
either DNS support or profile configuration.  But locate plugins could
provide the ability to find KDCs, and some libkrb5 operations (such as
IAKERB initiation) could succeed without needing to locate KDCs.

Also get rid of the profile_in_memory context flag, since we don't use
it any more.
Remove BADSYMS

We haven't been using it or keeping it up to date, and there's no
need to keep it checked in.