How to remove Minecraft Villager Careers from their Trading Interface

If you mean just the display name, then a custom name will replace it:

/summon Villager ~ ~1 ~ {CustomName:"A Villager",Career:1}

If you mean to prevent careers from affecting trades (since trading will refresh trades based on their career), then you need to set their "Career" to a non-0 value that also corresponds to their "Profession" (a value of 1 covers all professions), as well as set their "CareerLevel" to a value higher than the 'maximum' level for that career (which varies).

For example, the following villager will never create new trades.

/summon Villager ~ ~1 ~ {CustomName:"A Villager",Career:1,CareerLevel:100}