Revert "Updating GNU readline to 6.3."

This reverts commit dbaa07b8ef6cae1b726bc3bdbb9cfaca5116a2c3.

vcunat reported on IRC that the update breaks python and parted at least.
http://hydra.nixos.org/build/9661091/nixlog/1/tail-reload
Adding GNU readline 6.3 apart

I set bashInteractive to use it, as it has many relevant fixes.