Remove dev env futzing of supervisord.conf permissions

If we just link it into the dev env, we don't need to copy it at
startup, and we don't need write permissions on it.

installer/roles/image_build/templates/Dockerfile.j2

@@ -220,7 +220,6 @@ RUN for dir in \
       /vendor ; \
     do mkdir -m 0775 -p $dir ; chmod g+rw $dir ; chgrp root $dir ; done && \
     for file in \
-      /etc/supervisord.conf \
       /var/run/nginx.pid \
       /venv/awx/lib/python3.6/site-packages/awx.egg-link ; \
     do touch $file ; chmod g+rw $file ; done