Remove download-subtree method from JS (unused).
Remove download-subtree method from JS (unused).

N.B. This method (getDraftSubtree_url) is still used in server-side
Python! I'm just cleaning up unused JS in the pages.

OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree