Don't try to hide ambiguous usernames

[VAWVAW]

reasons

• users are still distinguished by color
• The names get loaded via plans anyway and worker.rs:members_insert doesn't check for ambiguous names so there is a race condition
• bridges to other chat platforms sometime have multiple puppet accounts with the same user name and just an id as a localpart which is useless for identifying the user to a human

alternatives

• fix the insert logic in members_insert and add a config option