dagutil: use revlog.parentrevs() for resolving parent revisions...
dagutil: use revlog.parentrevs() for resolving parent revisions
And remove parents() since it is no longer used.
revlog.parentrevs() is almost the same as parents(). The main
difference is that parentrevs() can return nullrev. dagop.headrevs()
already handles nullrev. We add an inline check for nullrev in the
other call site to account for the difference.
.. api:: parents() removed from dagutil classes
Use parentrevs() on the storage object instead.
Differential Revision:
https://phab.mercurial-scm.org/D4328
