patch 8.0.0241: fallback implementation of mch_memmove is unused

Problem:    Vim defines a mch_memmove() function but it doesn't work, thus is
            always unused.
Solution:   Remove the mch_memmove implementation. (suggested by Dominique
            Pelle)

src/misc2.c

@@ -1740,34 +1740,6 @@ vim_memset(void *ptr, int c, size_t size)
 }
 #endif
 
-/* skipped when generating prototypes, the prototype is in vim.h */
-#ifdef VIM_MEMMOVE
-/*
- * Version of memmove() that handles overlapping source and destination.
- * For systems that don't have a function that is guaranteed to do that (SYSV).
- */
-    void
-mch_memmove(void *src_arg, void *dst_arg, size_t len)
-{
-    /*
-     * A void doesn't have a size, we use char pointers.
-     */
-    char *dst = dst_arg, *src = src_arg;
-
-					/* overlap, copy backwards */
-    if (dst > src && dst < src + len)
-    {
-	src += len;
-	dst += len;
-	while (len-- > 0)
-	    *--dst = *--src;
-    }
-    else				/* copy forwards */
-	while (len-- > 0)
-	    *dst++ = *src++;
-}
-#endif
-
 #if (!defined(HAVE_STRCASECMP) && !defined(HAVE_STRICMP)) || defined(PROTO)
 /*
  * Compare two strings, ignoring case, using current locale.