wireprotoserver: access headers through parsed request Now that we can access headers via the parsed request object, let's do that. Since the new object uses bytes, hyphens, and is case-insensitive, a bit of code around normalizing values has been removed. I think the new code is much more intuitive because it more closely matches what is going out over the wire. Differential Revision: https://phab.mercurial-scm.org/D2743