stack/erp5: stop using caucase managed certificate for balancer

Revert "software/erp5: use a caucase managed certificate for balancer"

This reverts commit 74d18b9d and also follow
up fixup ( 555b26a2 ).

We are not ready to use caucase here, there are still too many problems with
caucase (keys are lost at each SR update etc) and design might still evolve,
so let's go back to self signed certificate for now.

Also remove the promise and the updater, since they are also not working and
causing problems on instances that have been updated (and where the key no
longer match the certificate)