blacklistd: Don't remove a ruleset if we have already added it

The noted argument is wrong - if it's already been deleted then the id we
have for it is invalid.
Because we don't track deletions to the ruleset, working it out is
problematic at best.

Instead, if we have already added the rule treat it as a non-op.

This is a valid use case because we might receive a burst of messages
in the downstream application for the same address and process them
one by one. It's not the job of the downstream application to track
blacklistd state.

Obtained from: https://github.com/zoulasc/blocklist/commit/959b18a6047c6facd100e5bb8a759eb597c65df2