Excess judgment

Author: Yadong Qi <qiyadong2010@gmail.com>

Closes #1629 from watermen/bug-fix2 and squashes the following commits:

59b7237 [Yadong Qi] Update HiveQl.scala

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala

@@ -610,7 +610,7 @@ private[hive] object HiveQl {
         // TOK_DESTINATION means to overwrite the table.
         val resultDestination =
           (intoClause orElse destClause).getOrElse(sys.error("No destination found."))
-        val overwrite = if (intoClause.isEmpty) true else false
+        val overwrite = intoClause.isEmpty
         nodeToDest(
           resultDestination,
           withLimit,