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

Author: Michael Armbrust <michael@databricks.com>

Closes #2323 from marmbrus/kryoJListNPE and squashes the following commits:

9634f11 [Michael Armbrust] Rollback JSON RDD changes
4d4d93c [Michael Armbrust] Merge remote-tracking branch 'origin/master' into kryoJListNPE
646976b [Michael Armbrust] Fix JSON RDD Conversion too
59065bc [Michael Armbrust] Remove explicit conversion to avoid NPE

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -460,7 +460,6 @@ class SQLContext(@transient val sparkContext: SparkContext)
       rdd: RDD[Array[Any]],
       schema: StructType): SchemaRDD = {
     import scala.collection.JavaConversions._
-    import scala.collection.convert.Wrappers.{JListWrapper, JMapWrapper}
 
     def needsConversion(dataType: DataType): Boolean = dataType match {
       case ByteType => true
@@ -482,8 +481,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
       case (null, _) => null
 
       case (c: java.util.List[_], ArrayType(elementType, _)) =>
-        val converted = c.map { e => convert(e, elementType)}
-        JListWrapper(converted)
+        c.map { e => convert(e, elementType)}: Seq[Any]
 
       case (c, ArrayType(elementType, _)) if c.getClass.isArray =>
         c.asInstanceOf[Array[_]].map(e => convert(e, elementType)): Seq[Any]