Remove the pre-fork GC.start

[byroot]

This doesn't actually help CoW friendliness, you'd need to run it 3 times for all objects to be promoted to the old generation.

But more importantly, you only want to do this before the very first fork, for any subsequent forks, it's best not to trigger GC.

Also GC.start can be quite taxing on large monolith, easily over 1s, which makes respawning dead workers slower and burn CPU for little to no gains.

In addition, modern Ruby versions have Process.warmup which does the same and more, but faster.

So ideally it would be preferable to expose a hook and let users decide what they want to do here.