Code review comment for lp:~tsarev/percona-server/test55_691404

1. What's the point to declare log-slow-admin-statements as OPT_ARG? What was wrong with NO_ARG?
2. What's the point in commenting out command line options in mysqld.cc instead of removing them? For this specific MP, it is sufficient to only remove log-slow-admin-statetements. There's no need to remove all of commented ones in this MP.