This switch is no longer necessary when only one command is given.
Internally completions are stored separately for each command,
so we only every print one command name per "complete" line anyway.
Currently, completions have to be specified like
```fish
complete -c foo -l opt
```
while
```fish
complete foo -l opt
```
just complains about there being too many arguments.
That's kinda useless, so we just assume if there is one left-over
argument that it's meant to be the command.
Theoretically we could also use *all* the arguments as commands to
complete, but that seems unlikely to be what the user wants.
(I don't think multi-command completions really happen)
Currently only `complete` will list completions, and it will list all
of them.
That's a bit ridiculous, especially since `complete -c foo` just does nothing.
So just make `complete -c foo` list all the completions for `foo`.
