revert --abort: do not leave behind useless sequencer-old directory

The "git cherry-pick --abort" command currently renames the
.git/sequencer directory to .git/sequencer-old instead of removing it
on success due to an accident.  cherry-pick --abort is designed to
work in three steps:

 1) find which commit to roll back to
 2) call "git reset --merge <commit>" to move to that commit
 3) remove the .git/sequencer directory

But the careless author forgot step 3 entirely.  The only reason the
command worked anyway is that "git reset --merge <commit>" renames the
.git/sequencer directory as a secondary effect --- after moving to
<commit>, or so the logic goes, it is unlikely but possible that the
caller of git reset wants to continue the series of cherry-picks that
was in progress, so git renames the sequencer state to
.git/sequencer-old to be helpful while allowing the cherry-pick to be
resumed if the caller did not want to end the sequence after all.

By running "git cherry-pick --abort", the operator has clearly
indicated that she is not planning to continue cherry-picking.  Remove
the (renamed) .git/sequencer directory as intended all along.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/revert.c

@@ -942,6 +942,7 @@ static int sequencer_rollback(struct replay_opts *opts)
 	}
 	if (reset_for_rollback(sha1))
 		goto fail;
+	remove_sequencer_state(1);
 	strbuf_release(&buf);
 	return 0;
 fail:

t/t7106-reset-sequence.sh

@@ -41,4 +41,12 @@ test_expect_success 'reset --hard cleans up sequencer state, providing one-level
 	test_path_is_missing .git/sequencer-old
 '
 
+test_expect_success 'cherry-pick --abort does not leave sequencer-old dir' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick base..anotherpick &&
+	git cherry-pick --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_path_is_missing .git/sequencer-old
+'
+
 test_done