Remove rb-readline

[hackartisan]

This gem makes it so that I can't use unicode strings in the pry console (see pry/pry-rails#69). @cwulfman Do you recall why you needed to add it?

[cwulfman]

I don't remember; it may have had something to do with creating zip files, but I see no evidence of it.

[hackartisan]

It's only installed in development so it would have been something specific to a local environment.

[cwulfman]

I think it can be removed. Would you like me to do it?

[hackartisan]

Okay thanks! I can do it.