strip out docker stuff, put into a plugin

app/controllers/admin/upgrade_controller.rb

@@ -1,20 +0,0 @@
-# EXPERIMENTAL: front end for upgrading your instance using the web UI
-
-class Admin::UpgradeController < Admin::AdminController
-
-  before_filter :ensure_admin
-  skip_before_filter :check_xhr
-
-  layout 'no_js'
-
-  def index
-    require_dependency 'upgrade/git_repo'
-    @main_repo = Upgrade::GitRepo.new(Rails.root)
-  end
-
-  protected
-
-  def ensure_admin
-    raise Discourse::InvalidAccess.new unless current_user.admin?
-  end
-end