mm: remove unnecessary description about a non-exist gfp flag

Since __GFP_NOACCOUNT was removed by commit 20b5c303 ("Revert 'gfp:
add __GFP_NOACCOUNT'"), its description is not necessary.
Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/gfp.h

@@ -105,8 +105,6 @@ struct vm_area_struct;
  *
  * __GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves.
  *   This takes precedence over the __GFP_MEMALLOC flag if both are set.
- *
- * __GFP_NOACCOUNT ignores the accounting for kmemcg limit enforcement.
  */
 #define __GFP_ATOMIC	((__force gfp_t)___GFP_ATOMIC)
 #define __GFP_HIGH	((__force gfp_t)___GFP_HIGH)