fuse: don't call dentry.InsertChild
fuse: don't call dentry.InsertChild

It is called from the kernfs code (OpenAt and revalidateChildLocked()).

For RemoveChildLocked, it is opposed. We need to call it from fuse.RmDir and
fuse.Unlink.

PiperOrigin-RevId: 333453218

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor