cli/packages: refactor doom-packages-purge
cli/packages: refactor doom-packages-purge

Sets it up for a later update where purging repos will no longer be the
default behavior.

hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/.emacs.d