test_practracker.sh python issues

It looks like we have a failure on Jenkins: https://jenkins.torproject.org/job/tor-ci-linux-master/ARCHITECTURE=amd64,SUITE=bullseye/4402/consoleFull

It seems like when we check-practracker-unit-tests, we try to run it even when we don't have python installed. Additionally, we don't set the PYTHON environment variable when we run check-pracktracker-unit-tests, so the script can look for python with the wrong name.

Both of these problems are solved if we remove check-practracker-unit-tests, I believe, since test_practracker.sh is already listed in TESTSCRIPTS, so we don't acutally need to have it in check-local as we thought in #32609 (moved)