Add a default delete override for the interface

include/grpc++/impl/codegen/async_unary_call.h

@@ -307,6 +307,11 @@ class default_delete<grpc::ClientAsyncResponseReader<R>> {
  public:
   void operator()(void* p) {}
 };
+template <class R>
+class default_delete<grpc::ClientAsyncResponseReaderInterface<R>> {
+ public:
+  void operator()(void* p) {}
+};
 }
 
 #endif  // GRPCXX_IMPL_CODEGEN_ASYNC_UNARY_CALL_H