[SPARK-4353][SQL] Delete the val that never used in Catalog

"dbName" in Catalog never used, like that 
{
   val (dbName, tblName) = processDatabaseAndTableName(databaseName, tableName)
   tables -= tblName 
}
i think it should be deleted,it should be "val tblName = processDatabaseAndTableName(databaseName, tableName)._2"