yum erase with --setopt instead of modifying yum.conf

Dockerfile

@@ -21,18 +21,8 @@ RUN GCCVER=6.1.0 && \
     ../gcc-$GCCVER/configure --disable-multilib --enable-languages=c,c++,fortran && \
     make -j `nproc` && \
     make install && \
-    echo 'clean_requirements_on_remove=1' >> /etc/yum.conf && \
-    yum erase -y gcc-c++ && \
+    yum erase -y gcc-c++ --setopt=clean_requirements_on_remove=1 && \
     yum clean all && \
     rm -rf /tmp/c6g6
 
 ENV LD_LIBRARY_PATH /usr/local/lib64${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}
-
-# uncomment the following to build julia as a test whether things work
-#RUN yum install -y which patch xz m4 cmake openssl-devel centos-release-scl && \
-#    yum install -y git19 python27 && \
-#    source /opt/rh/git19/enable && \
-#    source /opt/rh/python27/enable && \
-#    git clone https://github.com/JuliaLang/julia /tmp/julia && \
-#    cd /tmp/julia && \
-#    make -j `nproc` testall