rebase: delete unused p1 argument to _concludenode()
Unused since a0192a03216d (rebase: remove now unnecessary logic to
allow empty commit when branch changes, 2020-07-09).
Differential Revision: https://phab.mercurial-scm.org/D9055
#require rustfmt test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
$ RUSTFMT=$(rustup which --toolchain nightly rustfmt)
$ for f in `testrepohg files 'glob:**/*.rs'` ; do
> $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
> done