Problem : Multiple usernames are not useful

[MadanBhandari]

Problem : Multiple usernames are not useful

Solution :
Keep only one and unique username for every user.

Question : Is there any specific requirement for multiple usernames or use case ?

ping : @gazhayes

[anbud]

I believe they're used as nicknames for the mentioning system, I'm not sure if they should be removed.

[gsovereignty]

Yeah they are for mentions, so we need them