Revert "Override Docker ENTRYPOINT…"

[eyelidlessness]

When run with downstream images such as ODK Central's, the ENTRYPOINT change (#571) results in 404 responses from the transformation API endpoint. As we're preparing a release (#581), we're temporarily rolling back that change so we can investigate further.

[lognaturel]

FYI @jnm. We consider the image part of EE's public API so we'll want to make any changes that may require downstream images to change as part of a major release. ENTRYPOINT commands can't be overridden so any consumers that have used CMD in the past would have to change to ENTRYPOINT. This is likely surprising since node's own docs recommend using CMD: https://nodejs.org/en/docs/guides/nodejs-docker-webapp

We could consider a short-term likely fix of using the CMD exec form. This is what Central's image that uses EE's as a parent does and it does stop instantly. My understanding of the node images' docker-entrypoint.sh is that it directly runs commands with node if appropriate or otherwise essentially lets CMD override it.

Otherwise we do intend to change the Docker setup soon in a breaking way (enketo/enketo#935) and could include this change then if we really think ENTRYPOINT is appropriate.