Since commit 8ccb3caa it should be
more efficient to use page_id_t rather than two separate variables
for tablespace identifier and page number.

lock_rec_fold(): Replaced with page_id_t::fold().

lock_rec_hash(): Replaced with lock_sys.hash(page_id).

lock_rec_expl_exist_on_page(), lock_rec_get_first_on_page_addr(),
lock_rec_get_first_on_page(): Replaced with lock_sys.get_first().