Remove superfluous stuff from jupyterhub image

jupyterhub/Dockerfile

@@ -12,11 +12,9 @@ RUN apt-get update && \
 RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
     apt-get update && \
     apt-get install -y \
-        openssh-server \
         nodejs \
         node-gyp \
         libssl1.0-dev \
-        openbox \
         openjdk-11-jre-headless && \
     apt-get clean