kie-issues#654: simplify buildchain configuration

Author: jstastny-cz

.ci/buildchain-project-dependencies.yaml

@@ -8,12 +8,12 @@ dependencies:
       dependencies:
         default:
           - source: development
-            target: main # should migrate to 9 before the build
-          - source: 8.x # does not migrate
+            target: 9.x
+          - source: 8.x
             target: main
       dependant:
         default:
           - source: 9.x
             target: development
-          - source: main # should migrate to 9 before the build
-            target: development
+          - source: main
+            target: 8.x