[krbdev.mit.edu #7694] gsskrb5_extract_authz_data_from_sec_context misses AD-IF-RELEVANT containers

[Greg Hudson via RT]

gsskrb5_extract_authz_data_from_sec_context was added to make it possible 
to get the PAC from a sec context, and is currently the only interface 
shared between MIT krb5 and Heimdal for that purpose.  (The current 
preferred method, gss_get_name_attribute with the key "urn:mspac:", is not 
yet implemented in Heimdal.)

Unfortunately, gsskrb5_extract_authz_data_from_sec_context does not look 
inside AD-IF-RELEVANT containers, and PACs are now shipped in those 
containers.  So it's mostly useless for the intended purpose.  We should 
use krb5_find_authdata to find the authorization data element instead.