dirstate: remove _actual_file_name methode This is dead-code

revlog: add an exception hint when processing LFS flags without the extension It would be even better if this was either detected sooner, or the transaction completed (especially since the read/write processors aren't needed for the exchange). But this makes it easier for the user to resolve until that can be figured out.

tests: drop py36 conditionals in test-bad-extension.t Since this is a `>=` test, it's really conditionalizing py27 content, which isn't a thing anymore.