[SQL] Remove the duplicated code

Author: Cheng Hao <hao.cheng@intel.com>

Closes #4494 from chenghao-intel/tiny_code_change and squashes the following commits:

450dfe7 [Cheng Hao] remove the duplicated code

sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala

@@ -342,11 +342,6 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
         ExecutedCommand(
           RunnableDescribeCommand(resultPlan, resultPlan.output, isExtended)) :: Nil
 
-      case LogicalDescribeCommand(table, isExtended) =>
-        val resultPlan = self.sqlContext.executePlan(table).executedPlan
-        ExecutedCommand(
-          RunnableDescribeCommand(resultPlan, resultPlan.output, isExtended)) :: Nil
-
       case _ => Nil
     }
   }