mm/shmem: remove dead code can not be satisfied by "(CONFIG_SHMEM)&&(!(CONFIG_SHMEM))"

The value of “.fs_flags” in line 4608 is a dead code which will never
be implemented，because its conditions of line 47 "#ifdef CONFIG_SHMEM"
and line 4607 are mutually exclusive.  It is recommended to delete
redundant code.

Link: https://lkml.kernel.org/r/20230906045012.14999-1-sunying@nj.iscas.ac.cnSigned-off-by: Ying Sun <sunying@nj.iscas.ac.cn>
Suggested-by: Yanjie Ren <renyanjie01@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/shmem.c

@@ -4585,11 +4585,7 @@ static struct file_system_type shmem_fs_type = {
 	.parameters	= shmem_fs_parameters,
 #endif
 	.kill_sb	= kill_litter_super,
-#ifdef CONFIG_SHMEM
 	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP,
-#else
-	.fs_flags	= FS_USERNS_MOUNT,
-#endif
 };
 
 void __init shmem_init(void)