ovsdb-server: Remove the 'enable-dummy' option.

There is no use case of this option in ovsdb-server.  Also,
it causes dpif-dummy and netdev-dummy module register unrelated
unixctl commands.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
unixctl: Make command description all lowercase.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>