fix: git cache (#38763)

1. always use "last commit cache"
2. correctly build the cache key for any input (SafeCacheKey)
3. fix the git note "last commit cache FIXME" and avoid OOM

models/repo/repo.go

@@ -365,17 +365,6 @@ func (repo *Repository) APIURL(ctxOpt ...context.Context) string {
 	return httplib.MakeAbsoluteURL(ctx, setting.AppSubURL+"/api/v1/repos/"+url.PathEscape(repo.OwnerName)+"/"+url.PathEscape(repo.Name))
 }
 
-// GetCommitsCountCacheKey returns cache key used for commits count caching.
-func (repo *Repository) GetCommitsCountCacheKey(contextName string, isRef bool) string {
-	var prefix string
-	if isRef {
-		prefix = "ref"
-	} else {
-		prefix = "commit"
-	}
-	return fmt.Sprintf("commits-count-%d-%s-%s", repo.ID, prefix, contextName)
-}
-
 // LoadUnits loads repo units into repo.Units
 func (repo *Repository) LoadUnits(ctx context.Context) (err error) {
 	if repo.Units != nil {