remove x32 syscall timespec fixup hacks

remove x32 syscall timespec fixup hacks

the x32 syscall interfaces treat timespec's tv_nsec member as 64-bit
despite the API type being long and long being 32-bit in the ABI. this
is no problem for syscalls that store timespecs to userspace as
results, but caused uninitialized padding to be misinterpreted as the
high bits in syscalls that take timespecs as input.

since the beginning of the port, we've dealt with this situation with
hacks in syscall_arch.h, and injected between __syscall_cp_c and
__syscall_cp_asm, to special-case the syscall numbers that involve
timespecs as inputs and copy them to a form suitable to pass to the
kernel.

commit 40aa18d55ab763e69ad16d0cf1cebea708ffde47 set the stage for
removal of these hacks by letting us treat the "normal" x32 syscalls
dealing with timespec as if they're x32's "time64" syscalls,
effectively making x32 ax "time64-only 32-bit arch" like riscv32 will
be when it's added. since then, all users of syscalls that x32's
syscall_arch.h had hacks for have been updated to use time64 syscalls,
so the hacks can be removed.

there are still at least a few other timespec-related syscalls broken
on x32, which were overlooked when the x32 hacks were done or added
later. these include at least recvmmsg, adjtimex/clock_adjtime, and
timerfd_settime, and they will be fixed independently later on.