typing: make minor adjustments to mercurial/util.py to pass pytype checking I'm assuming the wrong-arg-count is a pytype bug, because this code is used by the config object. Avoiding initializing `_lrucachenode` node points to None eliminates a few `is not None` assertions, but apparently not all of them. I can't figure out why it gets confused over the state where these new assertions are. Differential Revision: https://phab.mercurial-scm.org/D10276