Wikipedia claims that it originated in Lisp, and the oldest reference I can find is this from 1991: https://www.dreamsongs.com/Files/LispGoodNewsBadNews.pdf (section 1.6.3)

In any case, before the JavaScript usage, it seems that treeshaking applied to objects to be included in a runtime image. The JavaScript usage is actually more akin to the dead-code elimination and link-time symbol removal of compiled and linked languages.

Interesting. It's come full circle terminology wise.