Fix memory leaks in payments home and confirm payment view models.

app/src/main/java/org/thoughtcrime/securesms/payments/confirm/ConfirmPaymentViewModel.java

@@ -101,6 +101,12 @@ final class ConfirmPaymentViewModel extends ViewModel {
     confirmPaymentRepository.confirmPayment(store.getState(), this::handleConfirmPaymentResult);
   }
 
+  @Override
+  protected void onCleared() {
+    super.onCleared();
+    store.clear();
+  }
+
   void refreshFee() {
     feeRetry.setValue(true);
   }

app/src/main/java/org/thoughtcrime/securesms/payments/preferences/PaymentsHomeViewModel.java

@@ -88,6 +88,12 @@ public class PaymentsHomeViewModel extends ViewModel {
     refreshExchangeRates(true);
   }
 
+  @Override
+  protected void onCleared() {
+    super.onCleared();
+    store.clear();
+  }
+
   private static PaymentsHomeState.PaymentsState getPaymentsState() {
     PaymentsValues paymentsValues = SignalStore.paymentsValues();