mm: update the description for madvise_remove

Currently, we have more filesystems supporting fallocate, e.g
ext4/btrfs.  Remove the outdated comment for madvise_remove.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/madvise.c

@@ -292,9 +292,6 @@ static long madvise_dontneed(struct vm_area_struct *vma,
 /*
  * Application wants to free up the pages and associated backing store.
  * This is effectively punching a hole into the middle of a file.
- *
- * NOTE: Currently, only shmfs/tmpfs is supported for this operation.
- * Other filesystems return -ENOSYS.
  */
 static long madvise_remove(struct vm_area_struct *vma,
 				struct vm_area_struct **prev,