samples: replace with symlink to test data

Instead of maintaining a separate set of samples that by now are very
much outdated (using Fedora 31 or older), make the samples directory
a symlink to the test data. Manifests in there are indeed tested and
maintained.
The error and noop samples are also covered in unit tests, so no need
for extra samples there either.

CI: remove the sample validation since all the test data manifests
    are actually built.

.github/workflows/tests.yml

@@ -66,28 +66,6 @@ jobs:
           test -d docs
           test -f docs/osbuild.1
 
-  sample_validation:
-    name: "sample validation"
-    runs-on: ubuntu-latest
-    container:
-      image: docker.io/library/python:3.7
-    steps:
-      - name: Clone repository
-        uses: actions/checkout@v2
-        with:
-          path: osbuild
-
-      - name: Install Dependencies
-        run: |
-          pip install jsonschema
-
-      - name: Validate the samples
-        run: |
-          cd osbuild
-          for f in samples/*; do
-            python3 -m osbuild --libdir . --inspect "$f" > /dev/null
-          done
-
   test_data:
     name: "Regenerate Test Data"
     runs-on: ubuntu-latest