[fusl] Remove code for unsupported architectures

fusl/arch/powerpc/bits/shm.h

-#define SHMLBA 4096
-
-struct shmid_ds {
-  struct ipc_perm shm_perm;
-  int __unused1;
-  time_t shm_atime;
-  int __unused2;
-  time_t shm_dtime;
-  int __unused3;
-  time_t shm_ctime;
-  int __unused4;
-  size_t shm_segsz;
-  pid_t shm_cpid;
-  pid_t shm_lpid;
-  unsigned long shm_nattch;
-  unsigned long __pad1;
-  unsigned long __pad2;
-};
-
-struct shminfo {
-  unsigned long shmmax, shmmin, shmmni, shmseg, shmall, __unused[4];
-};
-
-struct shm_info {
-  int __used_ids;
-  unsigned long shm_tot, shm_rss, shm_swp;
-  unsigned long __swap_attempts, __swap_successes;
-};