Remove workaround for setuptools issue

Latest version of setuptools is 60.7.1
https://setuptools.pypa.io/en/latest/history.html

On build and deploy of this cahnge this appears to
have fixed the problem identified for setuptools
version 50, here:
pypa/setuptools#2352

Dockerfile

@@ -55,10 +55,6 @@ ENV APP_GIT_COMMIT=${COMMIT_ID}
 ENV APP_BUILD_DATE=${BUILD_DATE}
 ENV APP_BUILD_TAG=${BUILD_TAG}
 
-# temporary "escape hatch" for setuputools > 50.0
-# https://github.com/pypa/setuptools/issues/2352
-ENV SETUPTOOLS_USE_DISTUTILS=stdlib
-
 # clearing data to prevent UNIQUE constraint violations when rebuilding locally, at least
 RUN python3 manage.py migrate --no-input \
     && python3 manage.py cleardata \