pscp: remove a relic of GUI feedback mode.

GUI feedback mode was last seen in 2006 (removed in commit 33b7caa59),
so quite what a conditioned-out piece of online help text for it was
doing still around here 12 years later, I have no idea.

(Especially since it had been under #if 0 since 2001, and also since
then its containing source file had ceased to be Windows-only so it
would have been extra-wrong to reinstate it.)

pscp.c

@@ -2257,17 +2257,6 @@ static void usage(void)
     printf("  -sshlog file\n");
     printf("  -sshrawlog file\n");
     printf("            log protocol details to a file\n");
-#if 0
-    /*
-     * -gui is an internal option, used by GUI front ends to get
-     * pscp to pass progress reports back to them. It's not an
-     * ordinary user-accessible option, so it shouldn't be part of
-     * the command-line help. The only people who need to know
-     * about it are programmers, and they can read the source.
-     */
-    printf
-	("  -gui hWnd GUI mode with the windows handle for receiving messages\n");
-#endif
     cleanup_exit(1);
 }