Remove dead uses of Puppet::Util::Cacher from autoloader

In the past, Puppet::Util::Autoload used a cached_attr for its 'searchpath'.
However, it no longer does that, so its references to Puppet::Util::Cacher are
unnecessary.

Reviewed-By: Jacob Helwig <jacob@puppetlabs.com>
(cherry picked from commit ce08cba9eb92abce7f7ab77dcf7eb9f9435d4040)