[python][client] Clean up samples and CI (#17509)

* chore: Remove leftover Github action file

This was probably added by mistake. A similar file is active in
.github/workflows/samples-python-pydantic-v1-petstore.yaml.

* chore: Remove leftover VERSION from old python-experimental sample

* ci: Stop running Python integration tests in Circle CI

These Python clients are all tested with Github Actions already, which
is faster, more cleanly separated and only runs on modifications.

I'm not cleaning up the pydantic-v1 client, I expect it to be removed soon anyway.

* chore: Remove true from sample folder name

python-disallowAdditionalPropertiesIfNotPresent-true
-> python-disallowAdditionalPropertiesIfNotPresent

samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/.github/workflows/python.yml

@@ -0,0 +1,38 @@
+# NOTE: This file is auto generated by OpenAPI Generator.
+# URL: https://openapi-generator.tech
+#
+# ref: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-python
+
+name: openapi_client Python package
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install flake8 pytest
+          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+          if [ -f test-requirements.txt ]; then pip install -r test-requirements.txt; fi
+      - name: Lint with flake8
+        run: |
+          # stop the build if there are Python syntax errors or undefined names
+          flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+          # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+          flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+      - name: Test with pytest
+        run: |
+          pytest