Revert "Override pythonpath in nodepool builder"

This reverts commit 515c29572190158428ac172febbf6871cf8977ee.

We found the reason why nodepool-builder wasn't starting was that when
we had the system-python and upstream-python installed at the same
version at the same time, the upstream-python was not built to use
relative libraries and hence started using the libpython.so from the
system-python.  This meant it was looking for libraries installed in
the system-python path (dist-packages) not the pip/upstream path
(site-packages).  This was reported and upstream are currently
evaluating a fix for that [1]

In the mean time, we merged Ib3dfda3df69e7ab359b96cd1865e47c7e1e8047b
which also avoids this problem by not including the "unstable" distro
in the image.  Since the system-python 3.11 packages were coming from
"unstable", this avoids the "same version" of the problem; the
upstream-python won't pick up the older version's libpython.so.

After this change the image is actually broken with this, because it
directs the system-python (now 3.9 since the change) to the 3.11
libraries, which obviously doesn't work.  Thus revert this now.

[1] https://github.com/docker-library/python/pull/785

Change-Id: I814d5920d8203bcb9f60b9769164c3d2a925f526

playbooks/roles/nodepool-builder/templates/docker-compose.yaml.j2

@@ -15,9 +15,6 @@ services:
       - DEBUG=1
       - STATSD_HOST=graphite.opendev.org
       - STATSD_PORT=8125
-      # TODO: remove once we fix the arm64 images using dist-packages
-      # instead of site-packages
-      - PYTHONPATH=/usr/local/lib/python311.zip:/usr/local/lib/python3.11:/usr/local/lib/python3.11/lib-dynload:/usr/local/lib/python3.11/site-packages
 
     volumes:
       # nodepool config