remove dead code

we don't recycle requests anymore, so we shouldn't need to recycle
cookie jars

actionpack/lib/action_dispatch/middleware/cookies.rb

@@ -396,11 +396,6 @@ def write(headers)
         @delete_cookies.each { |k, v| ::Rack::Utils.delete_cookie_header!(headers, k, v) }
       end
 
-      def recycle! #:nodoc:
-        @set_cookies = {}
-        @delete_cookies = {}
-      end
-
       mattr_accessor :always_write_cookie
       self.always_write_cookie = false