UserRebaseConfirmable: Remove feature flag
Rolled out through: 5f81d1ed (operations: Implement UserRebaseConfirmable in Go, 2021-03-12), UserRebaseConfirmable got a feature flag. This change removes the flag, and allows the removal of the Ruby code in 14.1.
Part of: #3575 (closed)
Edited by Zeger-Jan van de Weg