Ruby

Removed no longer used variable last_hash

1. By substituting n_var with its initializer, 0 < n_var is
   equivalent to argc > argi + n_trail.
2. As argi is non-negative, so argi + n_trail >= n_trail, and
   the above expression is equivalent to argc > n_trail.
3. Therefore, f_last is always false, and last_hash is no
   longer used.