Use github.com/saracen/walker for file walk operations

In some local tests w/ a slowed down filesystem, this massively cut down
on the time to clean up a repository by ~3x, bringing a total 'publish
update' time from ~16s to ~13s.

Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

api/files.go

@@ -170,11 +170,7 @@ func apiFilesListFiles(c *gin.Context) {
 	listLock := &sync.Mutex{}
 	root := filepath.Join(context.UploadPath(), utils.SanitizePath(c.Params.ByName("dir")))
 
-	err := filepath.Walk(root, func(path string, _ os.FileInfo, err error) error {
-		if err != nil {
-			return err
-		}
-
+	err := walker.Walk(root, func(path string, info os.FileInfo) error {
 		if path == root {
 			return nil
 		}