split: remove an unnecessary (and confusingly typed) fallback revision `opts.get('rev') or '.'` is either a list of strings or just a string. It happened to work because `'.'[0] == '.'` on Python 2, but it won't work on Python 3 (for byte strings). The fallback value wasn't even needed (it was also set just after), so let's just remove it.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate -I 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null