[SPARK-3447][SQL] Remove explicit conversion with JListWrapper to avoid NPE

Oh, after checking the code again, I think `.map(scalafy)` will convert the `JListWrapper` at here to an `ArrayBuffer` (`JListWrapper` is a  `Buffer` and `Buffer`'s `newBuilder` returns `ArrayBuffer`) and we will not have the Kryo issue. I tried `from pyspark.sql import SQLContext;SQLContext(sc).jsonRDD(sc.parallelize(['{"a":[3]}']))._jschema_rdd.collect()` and it's fine.