message: Fix BoundExpression deserialization
diff: @@ -49,15 +49,11 @@ public:
  writer.WriteOptional(expr);
  }
  - static unique_ptr<BoundExpression> Deserialize(Deserializer &source, ClientContext &context) {
  - FieldReader reader(source);
  - unique_ptr<Expression> expression;
  - expression = reader.ReadOptional<Expression>(move(expression), context);
  - return make_unique<BoundExpression>(move(expression));
  - }
  static unique_ptr<ParsedExpression> Deserialize(ExpressionType type, FieldReader &source, ClientContext& context) {
  - return make_unique<BoundExpression>(nullptr);
  + unique_ptr<Expression> expression;
  + expression = source.ReadOptional<Expression>(move(expression), context);
  + return make_unique<BoundExpression>(move(expression));
  }
  };
  