Remove the half-hearted attempt to make the utmp helper process drop

Remove the half-hearted attempt to make the utmp helper process drop
privileges just before dying of a fatal signal. I'm not sure what I
intended it for in the first place; it certainly isn't doing its job
properly (no setgid), it's causing compiler warnings due to not
checking the setuid return code, and we can't think of any useful
purpose for it.

git-svn-id: svn://svn.tartarus.org/sgt/putty@9766 cda61777-01e9-0310-a592-d414129be87e