Revert "Override Docker ENTRYPOINT so that PID 1 inside…" (#582)

This reverts commit 9f4d9aa.

Dockerfile

@@ -15,9 +15,4 @@ VOLUME ${ENKETO_SRC_DIR}/setup/docker/secrets
 
 EXPOSE 8005
 
-# Override the base image's ENTRYPOINT instead of passing arguments to it using
-# CMD, and use the "exec form" to avoid spawning an intermediary shell.
-# NB: Docker will not expand environment variables like ENKETO_SRC_DIR within
-# the ENTRYPOINT instruction; see
-# https://docs.docker.com/engine/reference/builder/#environment-replacement
-ENTRYPOINT ["/srv/src/enketo_express/setup/docker/start.sh"]
+CMD ${ENKETO_SRC_DIR}/setup/docker/start.sh