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.

[originally from svn r9766]

unix/uxpty.c

@@ -270,7 +270,6 @@ static void fatal_sig_handler(int signum)
 {
     putty_signal(signum, SIG_DFL);
     cleanup_utmp();
-    setuid(getuid());
     raise(signum);
 }
 #endif