manifest: Drop rpm-ostree by default

This came out of discussion in CentOS/centos-bootc-dev#27

Basically...I think what we should emphasize in the future
is the combination of `bootc` and `dnf`.

There's no really strong reason to use `rpm-ostree` at container
build time versus `dnf`.  Now on the *client* side...well,
here's the interesting thing; with transient root enabled,
`dnf install` etc generally just works.

Of course, *persistent* changes don't.  However, anyone who
wants that can just `dnf install rpm-ostree` in their container
builds.

There is one gap that's somewhat important which is kernel arguments.
Because we haven't taught `grubby` do deal with ostree, and
we don't have containers/bootc#255
to change kargs per machine outside of install time one will
need to just hand-edit the configs in `/boot/loader`.

Another fallout from this is that `ostree container` goes away
inside the booted host...and today actually this totally
breaks bib until osbuild/bootc-image-builder#18
is fixed.

Probably bootc should grow the interception for that too optionally.

tier-1/manifest.yaml

@@ -3,7 +3,6 @@ recommends: true
 
 include:
   - manifest-tier-0.yaml
-  - bootable-rpm-ostree.yaml
   - rpm-packaging.yaml
   - podman.yaml
   - firmware.yaml