bisect: simplify string_list memory handling

We declare the refs_for_removal string_list as NODUP, forcing us to
manually allocate strings we insert. And then when it comes time to
clean up, we set strdup_strings so that string_list_clear() will free
them for us.

This is a confusing pattern, and can be done much more simply by just
declaring the list with the DUP initializer in the first place.

It was written this way originally because one of the callsites
generated the item using xstrfmt(). But that spot switched to a plain
xstrdup() in the preceding commit. That means we can now just let the
string_list code handle allocation itself.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

bisect.c

@@ -1180,8 +1180,7 @@ int estimate_bisect_steps(int all)
 static int mark_for_removal(const struct reference *ref, void *cb_data)
 {
 	struct string_list *refs = cb_data;
-	char *bisect_ref = xstrdup(ref->name);
-	string_list_append(refs, bisect_ref);
+	string_list_append(refs, ref->name);
 	return 0;
 }
 
@@ -1190,16 +1189,15 @@ int bisect_clean_state(void)
 	int result = 0;
 
 	/* There may be some refs packed during bisection */
-	struct string_list refs_for_removal = STRING_LIST_INIT_NODUP;
+	struct string_list refs_for_removal = STRING_LIST_INIT_DUP;
 	refs_for_each_fullref_in(get_main_ref_store(the_repository),
 				 "refs/bisect/", NULL, mark_for_removal,
 				 &refs_for_removal);
-	string_list_append(&refs_for_removal, xstrdup("BISECT_HEAD"));
-	string_list_append(&refs_for_removal, xstrdup("BISECT_EXPECTED_REV"));
+	string_list_append(&refs_for_removal, "BISECT_HEAD");
+	string_list_append(&refs_for_removal, "BISECT_EXPECTED_REV");
 	result = refs_delete_refs(get_main_ref_store(the_repository),
 				  "bisect: remove", &refs_for_removal,
 				  REF_NO_DEREF);
-	refs_for_removal.strdup_strings = 1;
 	string_list_clear(&refs_for_removal, 0);
 	unlink_or_warn(git_path_bisect_ancestors_ok());
 	unlink_or_warn(git_path_bisect_log());