dillon1000/react

Remove beginWork shortcut

This shortcut had a bug associated with it. If beginWork on this
child returns null, then we don't call completeWork on that fiber.

Since removing this short cut adds another time check, we have to
add a single unit of time in tests to account for the top level
call now taking one more unit.

This was also the only recursive call in all of fiber so it's nice
to get rid of it to guarantee that a flat stack is possible.