Small refactoring of modules/private (#15947)

* Use correct variable name.

* doer is never nil here.

* Use status code constants.

* Replaced generic map with concrete struct.

* Fixed windows lint.

* Removed unused method.

* Changed error codes.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

services/repository/branch.go

@@ -26,7 +26,7 @@ func DeleteBranch(doer *models.User, repo *models.Repository, gitRepo *git.Repos
 		return ErrBranchIsDefault
 	}
 
-	isProtected, err := repo.IsProtectedBranch(branchName, doer)
+	isProtected, err := repo.IsProtectedBranch(branchName)
 	if err != nil {
 		return err
 	}