Apply suggestions from code review

Co-authored-by: Krzysztof Ligarski <63918941+kligarski@users.noreply.github.com>

Author: t0maboro

ios/RNSScreen.mm

@@ -949,7 +949,7 @@ - (void)invalidateImpl
   });
 }
 
-#ifndef RCT_NEW_ARCH_ENABLED
+#if !RCT_NEW_ARCH_ENABLED
 - (void)invalidate
 {
   [self invalidateImpl];

ios/RNSScreenStack.mm

@@ -1417,11 +1417,11 @@ - (void)mountingTransactionDidMount:(const facebook::react::MountingTransaction
           return;
         }
         for (RNSScreenView *screenRef : strongSelf->_toBeDeletedScreens) {
-#ifdef RCT_NEW_ARCH_ENABLED
+#if RCT_NEW_ARCH_ENABLED
           [screenRef invalidateImpl];
-#else
+#else // RCT_NEW_ARCH_ENABLED
           [screenRef invalidate];
-#endif
+#endif  // RCT_NEW_ARCH_ENABLED
         }
         strongSelf->_toBeDeletedScreens.clear();
       });