emsdk

Remove waterfall integration (#246)

We can remove this now that we have emscripten-releases working and use it everywhere we used the emsdk's waterfall integration.

In particular this should fix the current lkgr.json errors people are seeing (by removing all the lkgr stuff), which I believe started when I refactored that code while doing the releases work - I must have gotten something wrong on non-linux OSes. But anyhow, easier to remove that unnecessary code than fix it at this point.