kill apache_site

All that apache_site is doing is creating a symlink to the relevant file in
sites-available. The approach of the new apache module is to provision files
directly in sites-enabled rather than symlinks to files in sites-available.

Thus the following is true:

* Each apache_site resource has a corresponding
  File['/etc/apache2/sites-available/foo'] resource.
* By replacing sites-available with sites-enabled, the need for a symlink is
  gone, and the apache_site resource can be discarded.

Change-Id: Iddc778a28163947edef53a288bd986d0bfe2f309