fix: refresh mtime after remove file

https://github.com/vitalif/vitastor/pull/95

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src/nfs/nfs_kv_remove.cpp

@@ -282,6 +282,10 @@ resume_6:
             });
             return;
 resume_7:
+            if (!st->res)
+            {
+                st->self->parent->kvfs->touch_queue.insert(st->dir_ino);
+            }
             auto cb = std::move(st->cb);
             cb(st->res);
             return;