Remove g_mbstowcs() and g_wcstombs()

These calls are now replaced with explicit UTF conversion routines in
the common/string_calls.[hc] and common/parse.[hc] modules.

Also removed:-
- The support code in common/os_calls.c to set the locale to use
  these routines.
- The twchar type in arch.h

common/string_calls.c

@@ -710,30 +710,6 @@ g_strstr(const char *haystack, const char *needle)
     return (char *)strstr(haystack, needle);
 }
 
-/*****************************************************************************/
-int
-g_mbstowcs(twchar *dest, const char *src, int n)
-{
-    wchar_t *ldest;
-    int rv;
-
-    ldest = (wchar_t *)dest;
-    rv = mbstowcs(ldest, src, n);
-    return rv;
-}
-
-/*****************************************************************************/
-int
-g_wcstombs(char *dest, const twchar *src, int n)
-{
-    const wchar_t *lsrc;
-    int rv;
-
-    lsrc = (const wchar_t *)src;
-    rv = wcstombs(dest, lsrc, n);
-    return rv;
-}
-
 /*****************************************************************************/
 /* returns error */
 int