Stop installing unused tree command

There is no need to install the `tree` command into the container
image (some old version of the image may have used it, but this hasn't
been true for a while).

docker/Dockerfile

@@ -19,7 +19,7 @@ FROM ghcr.io/nginxinc/nginx-unprivileged:stable-alpine
 COPY --from=build /app/build /usr/share/nginx/html
 
 USER root
-RUN apk add --update tini tree
+RUN apk add --update tini
 COPY docker/nginx.conf /etc/nginx/conf.d/default.conf
 COPY docker/docker-entrypoint.sh /
 COPY docker/runtime-config-template.json /