Remove old sunk `start` tests
Remove old sunk `start` tests

The feature is now better specced (without relying on sleeps) in
https://github.com/perl6/roast/commit/9cf31a99c63a880596e68519999

Closes https://github.com/rakudo/rakudo/issues/2436 R#2436

dogbert17/roast,perl6/roast,dogbert17/roast