[SPARK-12003] [SQL] remove the prefix for name after expanded star

Right now, the expended start will include the name of expression as prefix for column, that's not better than without expending, we should not have the prefix.

Author: Davies Liu <davies@databricks.com>

Closes #9984 from davies/expand_star.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/unresolved.scala

@@ -204,7 +204,7 @@ case class UnresolvedStar(target: Option[Seq[String]]) extends Star with Unevalu
         case s: StructType => s.zipWithIndex.map {
           case (f, i) =>
             val extract = GetStructField(attribute.get, i)
-            Alias(extract, target.get + "." + f.name)()
+            Alias(extract, f.name)()
         }
 
         case _ => {