[core] Remove context from StateNodeConfig interface

[davidkpiano]

The context property has been removed from StateNodeConfig, as it has never been allowed, nor has it ever done anything. The previous typing was unsafe and allowed context to be specified on nested state nodes:

createMachine({
  context: {
    /* ... */
  }, // ✅ This is allowed
  initial: 'inner',
  states: {
    inner: {
      context: {
        /* ... */
      } // ❌ This will no longer compile
    }
  }
});

[Andarist]

This has tripped me a little bit. I know it will be a subject of a refactor in v5 so it doesn't matter - just want to leave a short comment for posterity.

The context has been removed from StateNodeConfig so I was wondering how this cast has produced a type that had a context property. StateMachine extends the StateNode class (and not the StateNodeConfig interface) which still has a context property:

xstate/packages/core/src/StateNode.ts

Line 494 in ce5a629

public get context(): TContext {