devel/py-ipykernel5: Remove in favor of devel/py-ipykernel

Ports were switched to devel/py-ipykernel5 on 2020-05-07
because devel/py-ipykernel has expired at the time.

Currently main consumers of devel/py-ipykernel - Jupyter and
Spyder - work fine with devel/py-ipykernel.

There is no reason to use an outdated devel/py-ipykernel5 everywhere.