Adjust removePools to not remove pools from the delisted set.

In response to review feedback:

#2277 (comment)

Author: jonathanknowles

lib/core/src/Cardano/Pool/DB/Model.hs

@@ -449,8 +449,6 @@ mRemovePools poolsToRemove = do
         $ Map.filterWithKey $ \(_, p) _ -> retain p
     modify #retirements
         $ Map.filterWithKey $ \(_, p) _ -> retain p
-    modify #delisted
-        $ Set.filter retain
   where
     retain p = p `Set.notMember` poolsToRemoveSet
     poolsToRemoveSet = Set.fromList poolsToRemove

lib/core/src/Cardano/Pool/DB/Sqlite.hs

@@ -505,7 +505,6 @@ newDBLayer trace fp timeInterpreter = do
             deleteWhere [ PoolRegistrationPoolId ==. pool ]
             deleteWhere [ PoolRetirementPoolId ==. pool ]
             deleteWhere [ StakeDistributionPoolId ==. pool ]
-            deleteWhere [ DelistedPoolId ==. pool ]
 
         removeRetiredPools epoch =
             bracketTracer traceOuter action