DEV: Drop duration column from topic timers (PR #13543)

The duration column has been ignored since the commit

for topic_timers, we use duration_minutes instead.

Also removing the duration key from Topic.set_or_create_timer. The only plugin to use this was discourse-solved, which doesn’t use it any longer since


I am not sure whether I remove this from the model in this PR or the next one? I am guessing I need another PR, because otherwise it will un-ignore the column before it is dropped?

Tricky… if it has already been ignored, we can technically drop this in a normal migration without any downsides but I don’t think our migration system allows that.

@tgxworld yeah I already tried dropping in a normal migration but it stopped me :frowning: Guess I will have to open another PR after this