Remove the duplicated function GetTags (#35375)

This PR removes the GetTags function from the git module and keeps only
GetTagInfos. All previous usages of GetTags have been replaced with
database-based tag functions.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/compare.go

@@ -707,12 +707,6 @@ func PrepareCompareDiff(
 }
 
 func getBranchesAndTagsForRepo(ctx gocontext.Context, repo *repo_model.Repository) (branches, tags []string, err error) {
-	gitRepo, err := gitrepo.OpenRepository(ctx, repo)
-	if err != nil {
-		return nil, nil, err
-	}
-	defer gitRepo.Close()
-
 	branches, err = git_model.FindBranchNames(ctx, git_model.FindBranchOptions{
 		RepoID:          repo.ID,
 		ListOptions:     db.ListOptionsAll,
@@ -721,7 +715,7 @@ func getBranchesAndTagsForRepo(ctx gocontext.Context, repo *repo_model.Repositor
 	if err != nil {
 		return nil, nil, err
 	}
-	tags, err = gitRepo.GetTags(0, 0)
+	tags, err = repo_model.GetTagNamesByRepoID(ctx, repo.ID)
 	if err != nil {
 		return nil, nil, err
 	}