Update puppet-catalog-test.gemspec to remove puppet dependency

removing dependency on puppet, since puppet is already installed via rpm.

In my environment, we install puppet via RPM.  When I install puppet-catalog-test via gem, I end up with puppet installed via gem as well.

Since puppet recommends the RPM install, can we install via RPM, this allows more to use this great tool. (http://docs.puppetlabs.com/guides/installation.html#installing-from-gems-not-recommended)