TBR croupier: Remove bad assert

This was a bad assert to place, since users should be able to pull
cards away from the passing cards section.

Change-Id: I0e0c14b678ab59988f79e222504a365821b98e21
diff --git a/lib/components/hearts/hearts.part.dart b/lib/components/hearts/hearts.part.dart
index ec39fa5..e539526 100644
--- a/lib/components/hearts/hearts.part.dart
+++ b/lib/components/hearts/hearts.part.dart
@@ -59,8 +59,6 @@
       } else if (dest == passingCards3) {
         passingCards3.clear();
         passingCards3.add(card);
-      } else {
-        assert("Unknown destination pile dest" == true);
       }
     });
   }