dom-updates: drop 'distroverpkg' from dnf.conf

It does nothing in dnf (was useful in yum era).

QubesOS/qubes-issues#4477

dom0-updates/patch-dnf-yum-config

@@ -73,8 +73,7 @@ EOF
 if [ -e /etc/dnf/dnf.conf ]; then
     update_conf /etc/dnf/dnf.conf "
 reposdir=/etc/yum.real.repos.d
-installonlypkgs = kernel, kernel-qubes-vm
+installonlypkgs = kernel, kernel-qubes-vm"
-distroverpkg = qubes-release"
 fi
 
 if [ -e /etc/yum.conf ]; then