refactor(registry): inline stable uid conflict check

registry/stable-uid.nix

@@ -22,13 +22,9 @@ in
 
   type = lib.types.ints.positive;
 
-  validate = entries:
+  validate = entries: [
-    let
-      uidConflicts = duplicateUids entries;
-    in
-    [
     {
-        assertion = uidConflicts == { };
+      assertion = duplicateUids entries == { };
       message = "Stable UID allocations must be unique.";
     }
   ];