[fusl] Remove code for unsupported architectures

fusl/arch/arm/bits/user.h

-typedef struct user_fpregs {
-  struct fp_reg {
-    unsigned sign1 : 1;
-    unsigned unused : 15;
-    unsigned sign2 : 1;
-    unsigned exponent : 14;
-    unsigned j : 1;
-    unsigned mantissa1 : 31;
-    unsigned mantissa0 : 32;
-  } fpregs[8];
-  unsigned fpsr : 32;
-  unsigned fpcr : 32;
-  unsigned char ftype[8];
-  unsigned int init_flag;
-} elf_fpregset_t;
-
-struct user_regs {
-  unsigned long uregs[18];
-};
-#define ELF_NGREG 18
-typedef unsigned long elf_greg_t, elf_gregset_t[ELF_NGREG];
-
-struct user {
-  struct user_regs regs;
-  int u_fpvalid;
-  unsigned long u_tsize, u_dsize, u_ssize;
-  unsigned long start_code, start_stack;
-  long signal;
-  int reserved;
-  struct user_regs* u_ar0;
-  unsigned long magic;
-  char u_comm[32];
-  int u_debugreg[8];
-  struct user_fpregs u_fp;
-  struct user_fpregs* u_fp0;
-};