revert: remove dangerous `parents` argument from `cmdutil.revert()`

Authored by martinvonz.


revert: remove dangerous parents argument from cmdutil.revert()

As we found out the hard way (thanks to spectral@ for figuring it
out!), cmdutil.revert()'s parents argument must be
repo.dirstate.parents() or things may go wrong. We had an extension
that passed in the target commit as the first parent. The hg split
command from the evolve extension seems to have made the same mistake,
but I haven't looked carefully.

The problem is that cmdutil._performrevert() calls
dirstate.normal() on reverted files if the commit to revert to
equals the first parent. So if you pass in ctx=foo and
parents=(foo.node(), nullid), then dirstate.normal() will be
called for the revert files, even though they might not be clean in
the working copy.

There doesn't seem to be any reason, other than a tiny performance
benefit, to passing the parents around instead of looking them up
again in cmdutil._performrevert(), so that's what this patch does.

Differential Revision: https://phab.mercurial-scm.org/D8925