Revert "Install etckeeper in step 1"

We don't want to institute a policy of having etckeeper everywhere,
it's a giant change that will have impact beyond just silencing this
warning.

This reverts commit 9a1c6136.

howto/upgrades/bookworm.md

@@ -53,7 +53,7 @@ See the "conflicts resolution" section below for how to handle
         : put server in maintenance &&
         touch /etc/nologin &&
         : install some dependencies
-        sudo apt install ttyrec screen debconf-utils deborphan etckeeper &&
+        sudo apt install ttyrec screen debconf-utils deborphan &&
         : create ttyrec file with adequate permissions &&
         sudo touch /var/log/upgrade-bookworm.ttyrec &&
         sudo chmod 600 /var/log/upgrade-bookworm.ttyrec &&