do not require rails its evil + cleanup other weird requires

`require 'securerandom' if defined?(SecureRandom)` etc does not make any sense to me ...

the usual railtie loads rails/railtie and not all of rails see https://github.com/rails/activemodel-globalid/blob/master/lib/active_model/railtie.rb and https://github.com/rails/activemodel-globalid/blob/master/lib/active_model/railtie.rb

@brianr @sbezboro