Fixes <https://issues.guix.gnu.org/67707>.
Previously ‘guix describe’ in the installation image would show the
URL of the local checkout that was used to build the image. It now
shows the default URL.
* gnu/system/install.scm (%installation-services): Change channel of
‘guix’ package to inherit from ‘%default-guix-channel’.
Change-Id: If848b5a6166904e982e0f9a0780f3e3f53bdfc28