dillon1000/react

Quick fix for ReactScheduler type inconsistency (#12828)

**what is the change?:**
In some cases we had defined the 'callback' as taking two arguments,
when really we meant to indicate the second argument passed to
'scheduleWork'.

**why make this change?:**
For correctness and to unblock something @gaearon is working on. A bit
surprised Flow didn't catch this in the first place.

**test plan:**
Ran tests, flow, lint.