code: public void deleteBranch(Serializable projectId, String branchName) throws IOException {
          String tailUrl = GitlabProject.URL + "/" + sanitizeProjectId(projectId) + GitlabBranch.URL + '/' + sanitizePath(branchName);
          retrieve().method(DELETE).to(tailUrl, Void.class);
      }
docs: Delete Branch.
  
  @param projectId  The id of the project
  @param branchName The name of the branch to delete
  @throws IOException on gitlab api call error