Don't send ENABLE_PUSH set to 1.
Don't send ENABLE_PUSH set to 1.

For some strange reason nghttp2 seems not to like it, and I haven't
worked out whether or not that's my fault or theirs yet. Either way,
they're a lot bigger than we are, so let's assume they're right and not
send it. Tracked by tatsuhiro-t/nghttp2#39.

fredthomsen/hyper,plucury/hyper,masaori335/hyper,jdecuyper/hyper,masaori335/hyper,Lukasa/hyper,irvind/hyper,Lukasa/hyper,fredthomsen/hyper,lawnmowerlatte/hyper,plucury/hyper,lawnmowerlatte/hyper,irvind/hyper,jdecuyper/hyper