templater: move function table to the "context" object Prepares for splitting template functions from templater.py.

hgweb: remove wsgirequest (API) Good riddance. .. api:: The old ``wsgirequest`` class for handling everything WSGI in hgweb has been replaced by separate request and response types. Various high-level functions in the hgweb WSGI applications now receive these new types as arguments instead of the old ``wsgirequest`` type. Differential Revision: https://phab.mercurial-scm.org/D2832