Remove UserGuide before 0.13 from website

[Jialin Qiao]

Hi,

There are 8 versions UserGuide on our website[1], the old versions are
hardly used anymore.

I prefer to remove the history versions before 0.13 (not include).

[1] https://iotdb.apache.org/

Thanks,
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Jialin Qiao
Apache IoTDB PMC