Removed Runnable, which is no longer being used.

Author: jdantonio

lib/concurrent.rb

@@ -22,7 +22,6 @@
 require 'concurrent/observable'
 require 'concurrent/options_parser'
 require 'concurrent/promise'
-require 'concurrent/runnable'
 require 'concurrent/scheduled_task'
 require 'concurrent/supervisor'
 require 'concurrent/timer_task'

lib/concurrent/runnable.rb

@@ -1,7 +1,6 @@
 require 'thread'
 
 require 'concurrent/errors'
-require 'concurrent/runnable'
 
 module Concurrent