pack-bitmap: drop redundant args from bitmap_writer_build_type_index()

The previous commit ensures that the bitmap_writer's "to_pack" field is
initialized early on, so the "to_pack" and "index_nr" arguments to
`bitmap_writer_build_type_index()` are redundant.

Drop them and adjust the callers accordingly.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -1345,7 +1345,7 @@ static void write_pack_file(void)
 						   the_repository, &to_pack);
 				bitmap_writer_set_checksum(&bitmap_writer, hash);
 				bitmap_writer_build_type_index(&bitmap_writer,
-					&to_pack, written_list, nr_written);
+							       written_list);
 			}
 
 			if (cruft)