Remove Codecov Integration

[Chrimle]

As Codecov is not functioning properly, and that the uploaded Jacoco Test Coverage Reports states 0% test coverage, this integration provides no value. The integration will be removed entirely, as Codecov will falsely comment on each commit warning about lack of test coverage.

This reverts commit 5365bb6ad076b11542ecc5d3d365f5efe66e6b88.

Checklist

• [x] Closes #215
• [ ] ~Documentation (README.md) has been updated~
• [ ] ~Version number updated in pom.xml and licenseInfo.mustache~
• [ ] ~Project has been compiled with mvn clean install~
• [ ] ~Updated generated-sources-files have been committed~

[Chrimle]

• [x] Remove the CODECOV secret!

[Chrimle]

CODECOV_TOKEN secret removed :heavy_check_mark: