get rid of "__test_target__" et al

[melange396]

many (if not all) of our integration and unit test files include the setting of a variable "__test_target__". it is also frequently accompanied by a comment of a form similar to "# py3tester coverage target (equivalent to `import *`)". they are no longer needed as we removed our dependence on py3tester a while ago. since then, we have even superstitiously perpetuated these code snippets in new test files created.

py3test references should also be yeeted from the following files:

.github/workflows/ci.yaml
deploy.json
dev/docker/python/setup.sh
dev/local/install.sh
dev/local/setup.cfg
docs/new_endpoint_tutorial.md
docs/epidata_development.md

this is a subset of what i mentioned in a comment on issue 965

[melange396]

an additional bonus to this would be that development docker images will be smaller and build faster!

[krivard]

does github-deploy-repo run py3tester or pytest?

if it runs pytest then we can slap help-wanted on this; if it runs py3tester that may require a bit more work

[dshemetov]

FWIW, I tried removing these before and ran into errors. I don't remember 100%, but I think the errors were only on staging, not in Docker unit/integration tests, which makes me think some part of github-deploy-repo still uses py3tester. See this thread for a recent failure due to this. We may have turned off py3tester there or maybe it was a TODO, not sure?