Revert "Merge pull request #534 from keisuke-umezawa/feature/introduce-python-coverage"

This reverts commit 0f4fc37fca, reversing
changes made to a7cf1d8f68.

.github/workflows/python-coverage.yml

@@ -1,44 +0,0 @@
-name: python coverage
-
-on:
-  push:
-    branches:
-      - master
-  pull_request: {}
-
-jobs:
-  coverage:
-    runs-on: ubuntu-latest
-    steps:
-    - name: Checkout
-      uses: actions/checkout@v3
-
-    - name: Setup Python
-      uses: actions/setup-python@v4
-      with:
-        python-version: '3.10'
-        architecture: x64
-
-    - name: Install dependencies
-      run: |
-        python -m pip install --progress-bar off --upgrade pip setuptools
-        pip install --progress-bar off .[optional]
-        pip install --progress-bar off .[test]
-        pip install --progress-bar off "optuna>=3.0.0"
-        pip install --progress-bar off .
-        echo 'import coverage; coverage.process_startup()' > sitecustomize.py
-
-    - name: Tests
-      env:
-        PYTHONPATH: .  # To invoke sitecutomize.py
-        COVERAGE_PROCESS_START: .coveragerc  # https://coverage.readthedocs.io/en/6.4.1/subprocess.html
-        COVERAGE_COVERAGE: yes  # https://github.com/nedbat/coveragepy/blob/65bf33fc03209ffb01bbbc0d900017614645ee7a/coverage/control.py#L255-L261
-      run: |
-        coverage run --source=optuna_dashboard -m pytest python_tests
-        coverage combine
-        coverage xml
-
-    - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3
-      with:
-        file: ./coverage.xml