* Deal with mypy errors w/ type-hinted pynacl 1.5.0
Fixes#11644.
I really don't like that we're monkey patching pynacl SignedKey
instances with alg and version objects. But I'm too scared to make the
changes necessary right now.
(Ideally I would replace `signedjson.types.SingingKey` with a runtime class which
wraps or inherits from `nacl.signing.SigningKey`.) C.f. https://github.com/matrix-org/python-signedjson/issues/16
Part of #9744
Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.
`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>`
