refactor(platform): Make git to be class-less (#6635)

lib/manager/composer/artifacts.spec.ts

lib/manager/gomod/artifacts.spec.ts

lib/manager/pipenv/artifacts.spec.ts

lib/platform/azure/index.spec.ts

lib/platform/azure/index.ts

lib/platform/bitbucket-server/index.spec.ts

lib/platform/bitbucket-server/index.ts

lib/platform/bitbucket-server/types.ts

lib/platform/bitbucket/index.spec.ts

lib/platform/bitbucket/index.ts

lib/platform/bitbucket/utils.ts

lib/platform/git/index.ts

lib/platform/gitea/index.spec.ts

lib/platform/gitea/index.ts

lib/platform/github/index.spec.ts

lib/platform/github/index.ts

lib/platform/github/types.ts

lib/platform/gitlab/index.spec.ts

lib/platform/gitlab/index.ts

lib/platform/index.ts