As pointed out by faho, the completions will be deduplicated by the completion
mechanics. We don't use this list directly except to pass it up the chain to the
shell, so there's no benefit to shelling out to eagerly deduplicate the list.
Plus, as of 3.6.0, even manual `complete -C"..."` invocations now deduplicate
results the same as if completions were triggered.
`fail2ban-client` uses nested subcommand syntax and intermixes fixed/enumerable
values with dynamically detected ones. If you know exactly what your overall
command structure looks like, these completions will work great. Unfortunately
their discoverability is a bit lacking, but that's not really fish's fault.
e.g.
* `f2b-c get/set` take certain known values but also accepts a dynamic jail name
* `f2b-c get/set <jail>` take certain fixed options but...
* `f2b-c get/set <jail> action` require enumerating an entirely different set
of values to generate the list of completions, bringing us to...
* `f2b-c get <jail> action <action>` has a fixed number of options but
* `f2b-c set <jail> action <action> <property>` can be any valid command and its
arguments
The intermixing of fixed, enumerable, and free-form inputs in a single command
line is enough to make one's head spin!
