s390x: fix fpreg_t and remove unused per_struct

Including sys/procfs.h complains unknown type name 'fpreg_t' in
bits/user.h. fpreg_t in bits/signal.h and elf_fpreg_t in bits/user.h
are practically the same.

per_struct is never used, even conflicts with kernel header
asm/ptrace.h
1 file changed