Remove unused configuration key

config/default.rb

@@ -2,7 +2,6 @@ Vagrant::Config.run do |config|
   # default config goes here
   config.vagrant.dotfile_name = ".vagrant"
   config.vagrant.host = :detect
-  config.vagrant.ssh_session_cache = false
 
   config.ssh.username = "vagrant"
   config.ssh.password = "vagrant"

lib/vagrant/config/vagrant.rb

@@ -3,7 +3,6 @@ module Vagrant
     class VagrantConfig < Base
       attr_accessor :dotfile_name
       attr_accessor :host
-      attr_accessor :ssh_session_cache
 
       def validate(env, errors)
         [:dotfile_name, :host].each do |field|