Test: cts: Drop -l/--limit-nodes option from cts-lab

It was added in 2005 by commit 0dbd70f. At the time, the node list was
built from /etc/ha.d/ha.cf, rather than from a --nodes CLI option. I
could see it maybe being convenient to store a list of all available
nodes in a config file and use only the first X of them as desired.
However, I don't see much of a use case for --limit-nodes now. If you
want fewer nodes, pass fewer nodes on the command line.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>