message: Bring back removal of empty entries.
diff: @@ -306,6 +306,7 @@ impl<I> LinearChain<I> {
  if let Some(validator_sigs) = self.pending_finality_signatures.get_mut(public_key) {
  validator_sigs.remove(&block_hash);
  }
  + self.remove_empty_entries();
  }
  }
  