Remove superfluous hardcode

docker/Dockerfile_centos_7.erb

@@ -30,7 +30,6 @@ RUN yum update -y -q \
     && yum install -y epel-release centos-release-scl \
     && sed -i 's|#[ \t]*baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-* \
     && sed -i 's|mirrorlist|#mirrorlist|g'  /etc/yum.repos.d/CentOS-* \
-    && sed -i 's|\$basearch|x86_64|g' /etc/yum.repos.d/CentOS-SCLo-scl* \
     && yum install -y -q \
          autoconf \
          automake \