Remove @plibdir from terminus install and name files explicitly

The terminus package shouldn't own the puppet lib dir, but rather just its own
files therein. This commit makes it so. It also removes the @plibdir
conditional in favor of a @pe conditional to help us move toward getting rid of
the OS-specific path templating in build artifacts.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>