do not duplicate the repo in OTHERMIRROR for Ubuntu

templates/etc/pbuilder/ubuntu.erb

@@ -2,7 +2,11 @@
 # pbuilder.
 
 MIRRORSITE=http://debian.stanford.edu/ubuntu
-OTHERMIRROR="deb http://debian.stanford.edu/ubuntu <%= @distribution %> main multiverse restricted universe"
+
+# We do not set OTHERMIRROR. If we have a backports mirror we want to use
+# we can change this.
+# OTHERMIRROR="deb http://archive.ubuntu.com/ubuntu <%= @distribution %>-backports main restricted universe multiverse"
+
 <%- if (@include_stanford_keyring) then -%>
 EXTRAPACKAGES="aptitude debconf-utils debhelper gnupg stanford-keyring"
 <%- else -%>
@@ -10,6 +14,7 @@ EXTRAPACKAGES="aptitude debconf-utils debhelper gnupg stanford-keyring"
 # Need to do this when CREATING the chroot; not needed for UPDATING.
 EXTRAPACKAGES="aptitude debconf-utils debhelper gnupg"
 <%- end -%>
+
 COMPONENTS="main multiverse restricted universe"
 
 DEBOOTSTRAPOPTS=("${DEBOOTSTRAPOPTS[@]}" "--keyring=/usr/share/keyrings/ubuntu-archive-keyring.gpg")