Remove the argument previously added for CachedCookbook#pretty_print

Since pretty_print is the interface for the stdlib PP class, there was
some confusion over what this method was for. The last commit wasn't
the place to fix it though, so removing for now.

Signed-off-by: Evan Owen <kainosnoema@gmail.com>
Use the more semantically correct #collect instead of #map

Signed-off-by: Evan Owen <kainosnoema@gmail.com>