singleNodeTestConfigWith: properly use Genesis window

The unused `_eraParams` binding is likely an accidental leftover.

The actual Genesis tests aren't affected as they use their own custom config
defined in `Test.Consensus.PeerSimulator.Config`.

ouroboros-consensus/src/unstable-consensus-testlib/Test/Util/TestBlock.hs

@@ -624,14 +624,12 @@ singleNodeTestConfigWith codecConfig storageConfig k genesisWindow = TopLevelCon
 
     ledgerCfgParams :: TestBlockLedgerConfig
     ledgerCfgParams = TestBlockLedgerConfig {
-      tblcHardForkParams = HardFork.defaultEraParams k slotLength,
+      tblcHardForkParams = (HardFork.defaultEraParams k slotLength) {
+          HardFork.eraGenesisWin = genesisWindow
+        },
       tblcForecastRange = SNothing
     }
 
-    _eraParams :: HardFork.EraParams
-    _eraParams = (HardFork.defaultEraParams k slotLength) {HardFork.eraGenesisWin = genesisWindow}
-
-
 {-------------------------------------------------------------------------------
   Test blocks without payload
 -------------------------------------------------------------------------------}