removed last update time because to continuous conversion.

"Time.now" might not be suitable to continue execution
It updates configuration at every chef run.


### example

```
  * template[/etc/ipf/ipf.conf] action create
    - update template[/etc/ipf/ipf.conf] from e30ebc to e8dfd6
        --- /etc/ipf/ipf.conf   2013-06-27 09:11:16.951118331 +0000
        +++ /tmp/chef-rendered-template20130627-77205-d4ifqx    2013-06-27 09:11:42.021439867 +0000
        @@ -1,5 +1,5 @@
         ## This file was written by Chef.  Do not edit by hand.
        -## Dropped off around 2013-06-27 09:11:16 +0000
        +## Dropped off around 2013-06-27 09:11:42 +0000
         ## via recipe[ipf::default] /var/chef/cache/cookbooks/ipf/recipes/default.rb:56
```