bisect: remove BISECT_NAMES after done.

I noticed that we forgot to clean this file and kept it that
way, while trying to help with Andrew's bisect problem.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/git-bisect.sh b/git-bisect.sh
index 51e1e44..0750253 100755
--- a/git-bisect.sh
+++ b/git-bisect.sh
@@ -172,6 +172,7 @@
 	rm -fr "$GIT_DIR/refs/bisect"
 	rm -f "$GIT_DIR/refs/heads/bisect"
 	rm -f "$GIT_DIR/BISECT_LOG"
+	rm -f "$GIT_DIR/BISECT_NAMES"
 }
 
 bisect_replay () {