rm unnecessary dockerfile for flask_metrics. we will use the dockerfile from the monitor instead

docker/flask_metrics/Dockerfile

@@ -1,31 +0,0 @@
-FROM      python:3.9-slim
-WORKDIR   /srv/newsblur
-ENV       PYTHONPATH=/srv/newsblur
-COPY      flask_metrics/requirements.txt /srv/newsblur/
-RUN       set -ex \
-          && rundDeps=' \
-                  libpq5 \
-                  libjpeg62 \
-                  libxslt1.1 \
-                            ' \
-          && buildDeps=' \
-                    patch \
-                    python-dev \
-                    gfortran \
-                    lib32ncurses5-dev  \
-                    libblas-dev \
-                    libffi-dev \
-                    libjpeg-dev \
-                    libpq-dev \
-                    libreadline6-dev \
-                    liblapack-dev \
-                    libxml2-dev \
-                    libxslt1-dev \
-                    ncurses-dev \
-                    zlib1g-dev \
-                            ' \
-            && apt-get update \
-            && apt-get install -y $rundDeps $buildDeps --no-install-recommends \
-            && pip install -r requirements.txt \
-            && apt-get purge -y --auto-remove ${buildDeps} \
-            && rm -rf /var/lib/apt/lists/*