Remove explicit readline

Author: janlelis

lib/irbtools/libraries.rb

@@ -36,7 +36,6 @@
   ObjectShadow.include(ObjectShadow::DeepInspect)
 end
 
-Irbtools.add_library 'readline', thread: :readline
 Irbtools.add_library 'os', thread: :os
 Irbtools.add_library 'ruby_engine', thread: :re
 Irbtools.add_library 'ruby_version', thread: :rv