Fix clang -Wunused-private-field

sql/item_func.h

@@ -1737,7 +1737,6 @@ class Item_func_set_user_var :public Item_func_user_var
        user variable it the first connection context).
   */
   my_thread_id entry_thread_id;
-  char buffer[MAX_FIELD_WIDTH];
   String value;
   my_decimal decimal_buff;
   bool null_item;

sql/sql_class.h

@@ -4565,7 +4565,6 @@ class select_insert :public select_result_interceptor {
 
 
 class select_create: public select_insert {
-  ORDER *group;
   TABLE_LIST *create_table;
   Table_specification_st *create_info;
   TABLE_LIST *select_tables;

sql/sql_load.cc

@@ -68,15 +68,13 @@ class READ_INFO {
   File	file;
   uchar	*buffer,			/* Buffer for read text */
 	*end_of_buff;			/* Data in bufferts ends here */
-  uint	buff_length,			/* Length of buffert */
-	max_length;			/* Max length of row */
+  uint	buff_length;			/* Length of buffert */
   const uchar *field_term_ptr,*line_term_ptr;
   const char  *line_start_ptr,*line_start_end;
   uint	field_term_length,line_term_length,enclosed_length;
   int	field_term_char,line_term_char,enclosed_char,escape_char;
   int	*stack,*stack_pos;
   bool	found_end_of_line,start_of_line,eof;
-  NET *io_net;
   int level; /* for load xml */