Remove docker_common clone

Docker_common, where 'entrypoint.sh' comes from, is
built inside the base image 'chbrandt/centos'.

dockerfile/Dockerfile

@@ -10,15 +10,9 @@ RUN source $HEASOFT_TMPDIR/install_heasoft.sh && \
     install && \
     rm -rf $HEASOFT_TMPDIR
 
-RUN git clone https://github.com/chbrandt/docker_commons.git && \
-    ln -sf docker_commons/entrypoint.sh /.
-
 COPY home $HEASOFT_TMPDIR
 RUN cat $HEASOFT_TMPDIR/non_interactive.rc \
         $HEASOFT_TMPDIR/ximage_exit_on_fail.rc \
         $HEASOFT_TMPDIR/ximage_no_history.rc \
     >> /etc/.bash_profile && \
     rm -rf $HEASOFT_TMPDIR
-
-ENTRYPOINT ["/entrypoint.sh"]
-