Always expand all services a saturation point applies to
open_fds was the only saturation point using allExcept, which
expanded to a negated selector in Prometheus, and a nested object in
JSON. This doesn't work well for Tamland, which assumes the list of
services will always be fully expanded.
As this was only used in one place, just remove the option to use
allExcept entirely. Instead, metricsCatalog.findServicesExcluding
can be used to much the same effect.