The benefit here is that external special remotes will need a
LISTCONFIGS request and response to generate their config parser,
and this avoids it being done for all the ones that don't have any
configs.
Note that, a config parser could in theory fail to parse if there are no
configs (none currently do), but a parse failure is already thrown away
when generating the remote list because it's too late. Such problems
have to be caught at initremote/enableremote time, not here.
e78bf29725