[chore] Remove sinatra env example isolation

This breaks jruby-rack when using :development gems, since `BUNDLE_WITHOUT` doesn't pass through and when initializing rack, jruby-rack tries to setup gems that have not been warbled since it ignores the BUNDLE_WITHOUT that warbler sets up.

Author: chadlwilson

examples/sinatra/config/warble.rb

@@ -6,5 +6,4 @@
   require 'socket'
   config.webxml.ENV_OUTPUT = File.expand_path('../../servers', __FILE__)
   config.webxml.ENV_HOST   = Socket.gethostname
-  config.webxml.jruby.runtime.env = false
 end