Revert "Void is not required to be `null` anymore."

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
diff --git a/runtime/vm/flow_graph_builder.cc b/runtime/vm/flow_graph_builder.cc
index 946978ea8f44ebdae6d7b26b1e5cb2c53e1a111a..53ae53b110010e69e75205afc4e2370c6aff297b 100644
--- a/runtime/vm/flow_graph_builder.cc
+++ b/runtime/vm/flow_graph_builder.cc
@@ -1259,9 +1259,8 @@ bool EffectGraphVisitor::CanSkipTypeCheck(TokenPosition token_pos,
     return false;
   }
 
-  // Any type is more specific than the dynamic type, the Object type, or void.
-  if (dst_type.IsDynamicType() || dst_type.IsObjectType() ||
-      dst_type.IsVoidType()) {
+  // Any type is more specific than the dynamic type and than the Object type.
+  if (dst_type.IsDynamicType() || dst_type.IsObjectType()) {
     return true;
   }