Remove a TODO in location_of_account_batch

Justification: we don't have a choice in this function because unlike
loading an account by location here we can't tell of an account whether
it's a new one or just wasn't loaded from parent.

It might have an implication to performance of transaction processing (I
do see some db lookups despite the fact that we preload a lot of stuff).
But I think we'll handle it via special-casing unsafe_preload
function, not right here.

src/lib/merkle_mask/masking_merkle_tree.ml

@@ -668,7 +668,6 @@ module Make (Inputs : Inputs_intf.S) = struct
           Base.location_of_account (get_parent t) account_id
 
     let location_of_account_batch t =
-      (* TODO consider handling special case of empty addresses *)
       self_find_or_batch_lookup
         (fun id -> (id, Option.map ~f:Option.some @@ self_find_location t id))
         Base.location_of_account_batch t