Revert "GPG module includes ruby::dev, which includes a conflicting build-essential pkg"

This reverts commit 982a9406666f076497ec22e1f34c9c3365056d49.

The gpg module no longer includes ruby::dev by default, so this should
not bring in a conflicting build-essential resource.

Conflicts:
	manifests/packages/extra.pp
(maint) Add gnupg-agent to extra packages

The gpg module no longer includes gnupg-agent, so this commit adds it
to the list of extra packages that we desire to have installed on a deb
builder.
Merge pull request #40 from haus/maint/master/add_back_gpg

(maint) Re-add gpg to extra packages