[fusl] Remove code for unsupported architectures

fusl/arch/powerpc/bits/user.h

-struct pt_regs {
-  unsigned long gpr[32], nip, msr, orig_gpr3, ctr, link, xer, ccr, mq;
-  unsigned long trap, dar, dsisr, result;
-};
-
-struct user {
-  struct pt_regs regs;
-  unsigned long u_tsize, u_dsize, u_ssize;
-  unsigned long start_code, start_data, start_stack;
-  long signal;
-  void* u_ar0;
-  unsigned long magic;
-  char u_comm[32];
-};
-
-#define ELF_NGREG 48
-#define ELF_NFPREG 33
-#define ELF_NVRREG 33
-typedef unsigned long elf_greg_t, elf_gregset_t[ELF_NGREG];
-typedef double elf_fpreg_t, elf_fpregset_t[ELF_NFPREG];
-typedef struct {
-  unsigned u[4];
-}
-#ifdef __GNUC__
-__attribute__((__aligned__(16)))
-#endif
-elf_vrreg_t,
-    elf_vrregset_t[ELF_NVRREG];