syscall: remove unused ptracePtr on openbsd

ptracePtr was introduced in CL 470299 for openbsd but it's not used on
this platform.

For #58387

Change-Id: I27901c3f4497e18dc407a9248b66e2691c9a6abb
Reviewed-on: https://go-review.googlesource.com/c/go/+/527535
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
Auto-Submit: Tobias Klauser <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: tklauser

src/syscall/syscall_openbsd_libc.go

@@ -67,7 +67,6 @@ func syscall9X(fn, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr,
 //sysnb execve(path *byte, argv **byte, envp **byte) (err error)
 //sysnb exit(res int) (err error)
 //sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
-//sys   ptracePtr(request int, pid int, addr unsafe.Pointer, data uintptr) (err error) = SYS_ptrace
 //sysnb getentropy(p []byte) (err error)
 //sys   fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
 //sys	fcntlPtr(fd int, cmd int, arg unsafe.Pointer) (val int, err error) = SYS_fcntl