f:ins with former f:st as child is displayed as struck out

[gerritbruening]

See
https://github.com/faustedition/faust-xml/blob/264f58b854cc292a56e16d10c52ed9116b95d649/xml/transcript/gsa/391098/0066.xml#L346
and

(http://dev.faustedition.net/document?sigil=2_H&page=66&view=document)
((just for future reference, not as an immediate task))