Do not check package freshness during upgrade.

Fixes <http://bugs.gnu.org/22740>.
Reported by Andreas Enge <andreas@enge.fr>.

* gnu/packages.scm (waiting, ftp-open*, check-package-freshness): Remove.
* guix/scripts/package.scm (options->installable): Adjust accordingly.
* emacs/guix-main.scm (package->manifest-entry*): Likewise.