In Chinese, we never use a single sex term to mean the whole job position that includes the opposite sex. For example, when policemen in English is used to mean the whole police force, it becomes politically incorrect. But in Chinese 警察 is unisex.
There are also
消防员 fire fighters male or female
发言人 spokesperson male or female
主席 chairperson male or female
So same here. 空姐 never means the whole flight attendant team, it only means female. And you cannot use it to mean male attendants. So there is no political problem here. As Jacky said, 空乘 is the word for the whole job position.