Only store master mey list in DAL handle

Only store master mey list in DAL handle

r24314 (#6778) created a hybrid owernship model for the master key
list, with one virtual copy stored in the DAL handle and one provided
to the caller of krb5_db_fetch_mkey_list.  Replace this with a model
where only the DAL handle owns the list, and a caller can get access
to an alias pointer with a new function krb5_db_mkey_list_alias().
Functions which previously accepted the master key list as an input
parameter now expect to find it in the DAL handle.

Patch by Will Fiveash <will.fiveash@oracle.com>.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25781 dc483132-0cff-0310-8789-dd5450dbe970