remove grammar makefile rules

I stumbled across this today, and it's not really working. It's been around for a very, very long time, and seems to be based on stuff we don't even have anymore. 

I asked in `#rust-internals`, and @cmr said we should just kill it, so here I am. :) I don't think that anything else uses Java, but maybe I missed something.

And if this _isn't_ what we want, I'm fine with closing too. Just some housekeeping.