RemoveEmptyStaves doesnt remove percussion staff

[neuro黃學仁]

How can one remove the empty percussion staff in Grandscore?
The \RemoveEmptyStaves seems not working on percussion staff.

Sample files can be reached at http://orchestra.tw/lilypond_Q
including:
00.ly
bdrum.ly
timp.ly
v1.ly
v2.ly

To run lilypond 00.ly (http://orchestra.tw/lilypond_Q/00.ly),
and it results in 00.pdf (http://orchestra.tw/lilypond_Q/00.pdf)

Thanks very much for any advise~

neuro
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