Changes

debian-buster-jenkins: remove pysim

This container is still used for osmo-gsm-tester_virtual (OS#6126).
pysim doesn't build anymore for some reason since the new dependency on
pyosmocom was added to it. Since we don't use pysim in osmo-gsm-tester,
simply don't install it in this container anymore.

Change-Id: I89f667fe5603526d9f0118fc338745aab8273070