Martin von Zweigbergk <martinvonz@google.com> [Fri, 25 Jan 2019 23:36:23 -0800] rev 41397
cleanup: use p1() and p2() instead of parents()[0] and parents()[1]
We have had these methods on both contexts and dirstate for a long
time now.
Differential Revision: https://phab.mercurial-scm.org/D5706