Drop more references of rbczmq_adapter

Author: rstammer

lib/iruby/session_adapter.rb

@@ -36,14 +36,12 @@ def make_rep_socket(protocol, host, port)
 
     require_relative 'session_adapter/ffirzmq_adapter'
     require_relative 'session_adapter/cztop_adapter'
-    require_relative 'session_adapter/rbczmq_adapter'
     require_relative 'session_adapter/pyzmq_adapter'
 
     def self.select_adapter_class(name=nil)
       classes = {
         'ffi-rzmq' => SessionAdapter::FfirzmqAdapter,
         'cztop' => SessionAdapter::CztopAdapter,
-        'rbczmq' => SessionAdapter::RbczmqAdapter,
         # 'pyzmq' => SessionAdapter::PyzmqAdapter
       }
       if (name ||= ENV.fetch('IRUBY_SESSION_ADAPTER', nil))