Synthesis of novel polyamides with hydantoin or 2‐thiohydantoin moieties from 2,2′‐alkylene‐ or arylenebis(1,3,4‐oxadiazolin‐5‐one)s and bis(1,3,4‐oxadiazoline‐5‐thione)s and dimethyl α,δ‐diaminoadipate dihydrochloride