fix TransactionCostData

Author: mihaieremia

src/entities/transactions/transaction-cost.ts

@@ -1,11 +1,6 @@
 import { ApiProperty } from '@nestjs/swagger';
 
-class TransactionCostData {
+export class TransactionCostData {
   @ApiProperty()
   txGasUnits!: number;
 }
-
-export class TransactionCost {
-  @ApiProperty()
-  data!: TransactionCostData;
-}