Replace struct update_lock_points with lambda

Summary:
No behavior change.
This code was introduced in 5add7a7 before we required C++11, which is
why the struct was needed. As we are now using more modern C++ and this
is the only place where lockpoints are updated for mempool entries, it
is more idiomatic to call `modify` with a lambda.

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

This concludes backport of [[bitcoin/bitcoin#23976 | core#23976]]
bitcoin/bitcoin@e177fca

Depends on D12587

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12588

src/txmempool.cpp

@@ -1551,7 +1551,8 @@ void DisconnectedBlockTransactions::updateMempoolForReorg(
             if (!validLP) {
                 // If CheckSequenceLocks succeeded, it also updated the
                 // LockPoints. Now update the mempool entry lockpoints as well.
-                pool.mapTx.modify(it, update_lock_points(lp));
+                pool.mapTx.modify(
+                    it, [&lp](CTxMemPoolEntry &e) { e.UpdateLockPoints(lp); });
             }
 
             // If the transaction spends any coinbase outputs, it must be

src/txmempool.h

@@ -322,15 +322,6 @@ class CompareTxMemPoolEntryByAncestorFee {
     }
 };
 
-struct update_lock_points {
-    explicit update_lock_points(const LockPoints &_lp) : lp(_lp) {}
-
-    void operator()(CTxMemPoolEntry &e) { e.UpdateLockPoints(lp); }
-
-private:
-    const LockPoints &lp;
-};
-
 // Multi_index tag names
 struct descendant_score {};
 struct entry_time {};