Refactor: cts-lab: Drop LogKind.ANY

It doesn't mean "any" within a LogWatcher object. It has that meaning
only as an initial value for the "log_kind" environment variable, which
gets assigned to watch_pref during log audits. It's clearer to use None
as the initializer.

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