Infra refactor: drop 'delphi' level of directory indirection from driver/repos

[krivard]

The directory tree for working in the backend has an extra level, delphi, which is not needed:

driver
    └── repos
        └── delphi
            └── delphi-epidata

Since moving from the custom py3tester package to the more-commonly-used pytest package, delphi is the only child of repos and can be removed.

As far as I can tell, driver/repos/delphi/delphi-epidata doesn't mirror the prod layout, so we don't need to worry about maintaining sync.

[melange396]

i believe this directory structure is an artifact of using https://github.com/cmu-delphi/github-deploy-repo, which probably means we should first take care of:

• Move acquisition deployment off of github-deploy-repo #1042

and then clean up the following...

the repos directory is assumed by two of our Dockerfiles:
https://github.com/cmu-delphi/delphi-epidata/blob/dev/dev/docker/python/Dockerfile (which calls https://github.com/cmu-delphi/delphi-epidata/blob/dev/dev/docker/python/setup.sh, that also references the dir) and
https://github.com/cmu-delphi/delphi-epidata/blob/dev/dev/docker/database/epidata/Dockerfile

https://github.com/cmu-delphi/delphi-epidata/blob/dev/dev/local/Makefile, which builds from those Dockerfiles, does too.

these two files for github actions mirror the behavior of the Makefile or use it directly:
https://github.com/cmu-delphi/delphi-epidata/blob/dev/.github/workflows/ci.yaml
https://github.com/cmu-delphi/delphi-epidata/blob/dev/.github/workflows/performance-tests.yml

and finally https://github.com/cmu-delphi/delphi-epidata/blob/dev/dev/local/install.sh which creates the initial directory structure and installs the Makefile.