Fix comment in virStorageBackendFileSystemRefresh

'.' and '..' are now skipped by virDirRead, there's no need to mention
them in the comment.

src/storage/storage_backend_fs.c

@@ -936,7 +936,7 @@ virStorageBackendFileSystemRefresh(virConnectPtr conn ATTRIBUTE_UNUSED,
                                                 &vol->target.encryption)) < 0) {
             if (err == -2) {
                 /* Silently ignore non-regular files,
-                 * eg '.' '..', 'lost+found', dangling symbolic link */
+                 * eg 'lost+found', dangling symbolic link */
                 virStorageVolDefFree(vol);
                 vol = NULL;
                 continue;