contrib/docker/centos7

largefiles: fix unused import

Caught by pyflakes.

FROM centos:centos7
RUN yum install -y gcc
RUN yum install -y python-devel python-docutils
RUN yum install -y make
RUN yum install -y rpm-build
RUN yum install -y gettext
RUN yum install -y tar
# For creating repo meta data
RUN yum install -y createrepo