gnu: pelican: Rearrange inputs.

* gnu/packages/python.scm (pelican)[native-inputs]: Remove
python-setuptools.
[propagated-inputs]: Move python-feedgenerator, python-jinja2,
python-pygments, python-docutils, python-pytz, python-blinker,
python-unidecode, python-six, python-dateutil-2 ...
[inputs]: ... to here.