nix: Remove broken docker-based nix development environment

It used to be possible to spin up a nix environment via docker container this way,
but the upstream nixos/nix image has changed and the docker build doesn't succeed
anymore. Since nobody complained about that, we can assume it is not being used
anyway.

nix/Dockerfile

@@ -1,22 +0,0 @@
-# This Dockerfile is only used as a development environment for
-# non-nix systems, i.e. Windows.
-
-FROM nixos/nix:latest
-
-RUN apk --no-cache add \
-    wget
-
-RUN nix-env -iA cachix -f https://cachix.org/api/v1/install \
- && cachix use postgrest
-
-# We need an unprivileged user here, to make PG run at all.
-RUN adduser --disabled-password --ingroup root nix \
- && chown -R nix:root /nix
-USER nix:root
-ENV USER=nix
-
-VOLUME /nix
-VOLUME /postgrest
-WORKDIR /postgrest
-
-CMD nix-shell

nix/docker-compose.yml

@@ -1,12 +0,0 @@
-version: '3'
-
-services:
-  nix:
-    container_name: postgrest-nix
-    build: .
-    volumes:
-      - ../:/postgrest
-      - nix:/nix
-
-volumes:
-  nix: