[krbdev.mit.edu #8816] kproplog cannot display LOCKDOWN_KEYS attribute

Ticket 8125 (commit 971fae8285427b27dfd8c9a535a18eb588ee0689) added 
krb5_flags_to_strings() and used it in kadmin.c, replacing the local 
flags table there.  It left alone the local flags table and 
print_flags() function in kproplog.c.

Ticket 8365 (commit 534db9834d6a77dc5e948e12844e72ba4e971e8c) added the 
lockdown_keys flag, but did not update the table in kproplog.c.

kproplog only displays attribute flags in double-verbose mode (-vv), so 
this omission is probably not noticeable, but for code hygiene the 
local flags table in kproplog should be removed in favor of 
krb5_flags_to_strings(), just as it was for kadmin.