Remove old migrations after forced upgraded

[joostjager]

Now that there has been a forced upgrade to at least lnd 0.14, can some of the 30 migrations be deleted?

[guggero]

I think that would be a good moment to get rid of some old code, yes. I don't know of any reason why we couldn't do it with something like 0.16.

[yyforyongyu]

I'd love to see those removed!

[joostjager]

I suppose everything pre-0.14 can go now?