syscall: update broken links

syscall: update broken links

Remove one link which isn't very interesting, and update another to
point to the current location.

Fixes #52753

Change-Id: I5f53ede35b0ded197bc0e6d41eabf28d736de5b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/405296
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Hajime Hoshi <hajimehoshi@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>