cleanup: run pyupgrade on our source tree to clean up varying things Built with: hg files 'set:**.py - mercurial/thirdparty/** - "contrib/python-zstandard/**" - hgext/fsmonitor/pywatchman/**' | xargs pyupgrade --keep-percent-format --keep-extraneous-parens and then blackened. pyupgrade comes from https://github.com/asottile/pyupgrade with a patch to let me preserve extraneous parens (which we use for marking strings that shouldn't be translated), and lets us clean up a bunch of idioms that have cruftily accumulated over the years. # skip-blame no-op automated code cleanups Differential Revision: https://phab.mercurial-scm.org/D8255