should not set wsgi_socket_prefix

The per-platform setting of wsgi_socket_prefix has been moved
into the Apache module - horizon should just include ::apache::mod::wsgi
Add a dependency on the version of puppetlabs-apache that sets the
default wsgi_socket_prefix for osfamily RedHat

Closes-Bug: #1374634
Change-Id: Iba8311ba25445d3367e71d3c0e854291c33e7258