Merge pull request #139 from c-bata/remove-codecov

Remove codecov workflow

Author: y0z

.github/workflows/coverage.yml

@@ -6,7 +6,6 @@ OptunaHub: A Platform for Black-Box Optimization
 [![Python](https://img.shields.io/badge/python-3.9%20%7C%203.10%20%7C%203.11%20%7C%203.12-blue)](https://www.python.org)
 [![pypi](https://img.shields.io/pypi/v/optunahub.svg)](https://pypi.python.org/pypi/optunahub)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/optuna/optunahub)
-[![Codecov](https://codecov.io/gh/optuna/optunahub/branch/main/graph/badge.svg)](https://codecov.io/gh/optuna/optunahub)
 
 
 :link: [**OptunaHub**](https://hub.optuna.org/)