Fixed #6850 - Clean up ResourceType#to_pson

There's no value in including the code when we convert a resource
type to JSON, since you can't convert it back again, so this removes
it.

I also cleaned up a few of the other attributes which were
producing unnecessary information.

Signed-off-by: Luke Kanies <luke@puppetlabs.com>
Reviewed-by: Daniel Pittman <daniel@puppetlabs.com>