Counters: forget the totals of objects that no longer exist

hc counters kept listing the objects of a configuration replaced since
housecarld started (an import with --replace gives every object a new
ID) beside the current ones. Disabled objects, built-ins and policies
keep their totals.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -42,6 +42,10 @@ All notable changes to Housecarl are documented here. The format follows
 
 ### Fixed
 
+- `hc counters` (`GET /counters`) kept listing the objects of a
+  configuration replaced since housecarld started (`hc import
+  --replace` gives every object a new ID), beside the current ones; the
+  totals of objects that no longer exist are now forgotten.
 - Import: two base chains on one hook had their rules imported twice,
   and the second chain's leading built-ins were moved above the first
   chain's rules; they now follow each other by priority (read in a