Wireless operators in Japan have begun to drop Huawei mobile phones after the US put the Chinese telecom-gear giant on a blacklist blocking it from buying vital US components.NTT Docomo, Japan’s largest operator, said on Wednesday it stopped taking pre-orders for Huawei’s new P30 handset, while its rival KDDI said it would indefinitely delay introduction of the phone, without elaborating.SoftBank’s YMobile announced a similar move, saying it is looking into concerns over the availability of…