Change the EDIT option of ruby to use libedit by default now that libedit
from ports is able to handle unicode. Make sure that ruby does not provides its
own function to read the input but let libedit do it itself.

This allows the binary package to by default not be "tainted" by the readline
license.

Differential Revision: https://reviews.freebsd.org/D1547
Reviewed by: swills
Approved by: ruby (swills)