Removing centos mirror for must-gather image (#596)

Author: deepakraj1997

must-gather/Dockerfile

@@ -5,7 +5,6 @@ RUN go get github.com/google/pprof
 FROM quay.io/openshift/origin-must-gather:4.7 as builder
 
 FROM registry.access.redhat.com/ubi8-minimal:latest
-RUN echo -ne "[centos-8-appstream]\nname = CentOS 8 (RPMs) - AppStream\nbaseurl = http://mirror.centos.org/centos-8/8/AppStream/x86_64/os/\nenabled = 1\ngpgcheck = 0" > /etc/yum.repos.d/centos.repo
 
 RUN microdnf -y install rsync tar gzip graphviz findutils