Summary:
`lfs` is the better large file solution. `largefiles` is rarely used, and
its implementation is less clean. So let's remove it.
Test Plan:
Ran all tests. A subrepo test was removed instead of cleaned up since the
longer term plan is to also drop subrepo support.
Reviewers: phillco, #mercurial
Reviewed By: phillco
Differential Revision: https://phabricator.intern.facebook.com/D6740361
Signature: 6740361:1516225594:555e3803571ad05e0434021897a2823ac99347ae
We store bytes in exc.args, which should be translated to a byte string
without encode/decode dance.
IOError subclasses are unchanged for now. We'll need to decide how our
IOErrors should be caught.