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

Fix compiler warning:
trx/trx0purge.c: In function 'trx_purge_rec_release':
trx/trx0purge.c:1007:18: error: variable 'arr' set but not used [-Werror=unused-but-set-variable]

storage/innobase/trx/trx0purge.c

@@ -1004,12 +1004,8 @@ trx_purge_rec_release(
 /*==================*/
 	trx_undo_inf_t*	cell)	/* in: storage cell */
 {
-	trx_undo_arr_t*	arr;
-
 	mutex_enter(&(purge_sys->mutex));
 
-	arr = purge_sys->arr;
-
 	trx_purge_arr_remove_info(cell);
 
 	mutex_exit(&(purge_sys->mutex));