Stop using git count-objects and use raw directory size for repository (#8848)

* Migrate from git count-objects to a raw directory size
* As per @guillep2k ignore unusual files

models/migrations/v28.go

@@ -60,9 +60,9 @@ func addRepoSize(x *xorm.Engine) (err error) {
 			}
 
 			repoPath := filepath.Join(setting.RepoRootPath, strings.ToLower(user.Name), strings.ToLower(repo.Name)) + ".git"
-			countObject, err := git.GetRepoSize(repoPath)
+			countObject, err := git.CountObjects(repoPath)
 			if err != nil {
-				log.Warn("GetRepoSize: %v", err)
+				log.Warn("CountObjects: %v", err)
 				continue
 			}