Remove duplicate env vars so that they may be overridden by the env file

For both dev/prod, the default settings file is set when the application is started:

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "ldvspec.settings.docker_sdc")

Additionally, the same setting is also (duplicately) present in the docker compose config for both dev and prod. Due to precedence of docker env settings (https://docs.docker.com/compose/environment-variables/envvars-precedence/), this makes it impossible to override this specific setting using the .env file on the system, and that is the purpose of this file in the first place.

By removing this env variable from the docker compose, it can now be overridden on a machine (e.g., to turn of profiling)