manifests: remove vars from fedora-build-v2

Defining variables in the build pipeline is potentially dangerous, because
it can lead to the buildroot using a different package set than the other
pipelines.

Thus, this commit removes the variables from the build manifest. Since now on,
the variables must be defined before the build manifest is included.

Since the build manifest is no longer buildable on its own, let's remove it
from mpp.yaml to ipp.yaml. This is a convention set by the automotive team:
ipp manifests are not meant to be directly buildable, they are only useful
for embedding.

test/data/manifests/fedora-uki.mpp.yaml

@@ -7,7 +7,7 @@ mpp-vars:
   updates: '20220801'
 pipelines:
   - mpp-import-pipeline:
-      path: fedora-build-v2.mpp.yaml
+      path: fedora-build-v2.ipp.yaml
       id: build
     runner:
       mpp-format-string: org.osbuild.fedora{release}