(partially) Fix Bug#55227 Fix compiler warnings in innodb with gcc 4.6

Fix compiler warnings:
trx/trx0roll.c: In function 'trx_undo_arr_remove_info':
trx/trx0roll.c:744:9: error: variable 'n' set but not used [-Werror=unused-but-set-variable]
trx/trx0roll.c:743:9: error: variable 'n_used' set but not used [-Werror=unused-but-set-variable]

storage/innodb_plugin/trx/trx0roll.c

@@ -740,13 +740,8 @@ trx_undo_arr_remove_info(
 	undo_no_t	undo_no)/*!< in: undo number */
 {
 	trx_undo_inf_t*	cell;
-	ulint		n_used;
-	ulint		n;
 	ulint		i;
 
-	n_used = arr->n_used;
-	n = 0;
-
 	for (i = 0;; i++) {
 		cell = trx_undo_arr_get_nth_info(arr, i);