wallet: provide WalletBatch to 'DeleteRecords'

So it can be used within an external db txn context.

src/wallet/scriptpubkeyman.cpp

@@ -2036,9 +2036,15 @@ std::optional<MigrationData> LegacyDataSPKM::MigrateToDescriptor()
 }
 
 bool LegacyDataSPKM::DeleteRecords()
+{
+    return RunWithinTxn(m_storage.GetDatabase(), /*process_desc=*/"delete legacy records", [&](WalletBatch& batch){
+        return DeleteRecordsWithDB(batch);
+    });
+}
+
+bool LegacyDataSPKM::DeleteRecordsWithDB(WalletBatch& batch)
 {
     LOCK(cs_KeyStore);
-    WalletBatch batch(m_storage.GetDatabase());
     return batch.EraseRecords(DBKeys::LEGACY_TYPES);
 }