Remove initialization of native_scno field for most of syscalls

Remove initialization of native_scno field for most of syscalls

The native_scno field is not so much used in the code than before.
In many cases sys_func is checked instead, and for most of syscall
entries there is no need to initialize native_scno.

* linux/i386/syscallent.h: Remove native_scno initialization for
_exit, read, write, waitpid, execve, wait4, sysfs, readv, writev,
pread64, pwrite64, exit_group, waitid, send, recv, sendto and
recvfrom syscall entries.
* linux/syscall.h: Do not define no longer used SYS_waitid and
SYS_sub_* constants.
[IA64]: Do not define SYS_waitpid and SYS32_* constants.
* defs.h: Do not define no longer used  __NR_exit_group constant.
* strace.c [USE_PROCFS] (proc_open): Use sys_func to check for execve.