nocmdline.c: remove unused stub of cmdline_process_param.

This was needed at the time it was introduced in commit
c99338b750, because uxputty.c (as was) handled its non-option
arguments directly (that was how Unix PuTTY and pterm arranged to have
different sets of them), and sometimes did it by converting them into
option arguments and feeding them to cmdline.c, so it still needed to
not fail to link when not linked against cmdline.c (for the
GtkApplication based front end).

But now the non-option argument handling is centralised into cmdline.c
itself, with a system of flags indicating which arguments a particular
tool expects. So that stub is no longer needed.

stubs/nocmdline.c

@@ -19,19 +19,3 @@ SeatPromptResult cmdline_get_passwd_input(prompts_t *p)
 {
     return SPR_INCOMPLETE;
 }
-
-/*
- * The main cmdline_process_param function is normally called from
- * applications' main(). An application linking against this stub
- * module shouldn't have a main() that calls it in the first place :-)
- * but it is just occasionally called by other supporting functions,
- * such as one in uxputty.c which sometimes handles a non-option
- * argument by making up equivalent options and passing them back to
- * this function. So we have to provide a link-time stub of this
- * function, but it had better not end up being called at run time.
- */
-int cmdline_process_param(const char *p, char *value,
-                          int need_save, Conf *conf)
-{
-    unreachable("cmdline_process_param should never be called");
-}