Remove WP.org image before submoduling the now-independent repo

debian/wp-org-deploy/Dockerfile

-FROM debian:stretch-slim
-
-LABEL maintainer="ethitter"
-LABEL version="1.0"
-
-RUN echo "deb http://security.debian.org/ stretch/updates main" >> /etc/apt/sources.list
-
-RUN apt-get update \
-    && apt-get -y --no-install-recommends install \
-        ca-certificates \
-        curl \
-        git \
-        rsync \
-        subversion \
-    && apt-get clean \
-    && rm -rf /var/lib/apt/lists/*