refactor: remove support for DOKKU_SCALE file

It has been replaced by the 'formations' key within the 'app.json' file format.

tests/apps/dockerfile-app-json-formations/Dockerfile

@@ -0,0 +1,13 @@
+FROM node:19-alpine
+
+RUN apk add --no-cache bash
+
+EXPOSE 3001/udp
+EXPOSE  3000/tcp
+EXPOSE 3003
+
+COPY . /app
+WORKDIR /app
+RUN npm install
+
+CMD npm start