s4:kdc: Fix memory leak for unused keys in TGT

s4:kdc: Fix memory leak for unused keys in TGT

Length of key list was reduced to one but unused keys were not deallocated before changing the length.
As such, free_sdb_entry/sdb_keys_free function could not release unused keys indexed from 1 onwards on entry deallocation.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15712

Signed-off-by: Ivan Korytov <korytovip@basealt.ru>
Reviewed-by: Jennifer Sutton <jennifersutton@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>