Migration screen is displayed for new users

[boreq]

Right now the migration screen shows up even for new users when they complete onboarding. This is just confusing (why is this thing migrating if I just installed it?) and effectively adds another screen to onboarding. The idea would be to dismiss the screen automatically if the migrations take longer then for example 10 seconds to run.

[mplorentz]

The title says the idea is to dismiss it if it's quick, but the description says

dismiss the screen automatically if the migrations take longer then for example 10 seconds to run
which sounds like the opposite to me?

It sounds like a bug that we show the migration screen or run migrations on a fresh install. Would it be a better fix to just not run this migration if there is no go-ssb data? Or we could detect that we are onboarding in Swift, assume the migration will be near-instant as there is nothing to migrate, and skip showing the screens.

[boreq]

I mean we can try not triggering the handlers if migrations determine that there is nothing to do but they have to be run to check if there is nothing to do. This will add a small complication to every migration but it is doable.