Adjust object format interface (#28469)

- Remove `ObjectFormatID`
- Remove function `ObjectFormatFromID`.
- Use `Sha1ObjectFormat` directly but not a pointer because it's an
empty struct.
- Store `ObjectFormatName` in `repository` struct

routers/api/v1/repo/repo.go

@@ -242,18 +242,18 @@ func CreateUserRepo(ctx *context.APIContext, owner *user_model.User, opt api.Cre
 	}
 
 	repo, err := repo_service.CreateRepository(ctx, ctx.Doer, owner, repo_service.CreateRepoOptions{
-		Name:          opt.Name,
-		Description:   opt.Description,
-		IssueLabels:   opt.IssueLabels,
-		Gitignores:    opt.Gitignores,
-		License:       opt.License,
-		Readme:        opt.Readme,
-		IsPrivate:     opt.Private,
-		AutoInit:      opt.AutoInit,
-		DefaultBranch: opt.DefaultBranch,
-		TrustModel:    repo_model.ToTrustModel(opt.TrustModel),
-		IsTemplate:    opt.Template,
-		ObjectFormat:  git.ObjectFormatFromID(git.Sha1),
+		Name:             opt.Name,
+		Description:      opt.Description,
+		IssueLabels:      opt.IssueLabels,
+		Gitignores:       opt.Gitignores,
+		License:          opt.License,
+		Readme:           opt.Readme,
+		IsPrivate:        opt.Private,
+		AutoInit:         opt.AutoInit,
+		DefaultBranch:    opt.DefaultBranch,
+		TrustModel:       repo_model.ToTrustModel(opt.TrustModel),
+		IsTemplate:       opt.Template,
+		ObjectFormatName: git.Sha1ObjectFormat.Name(),
 	})
 	if err != nil {
 		if repo_model.IsErrRepoAlreadyExist(err) {