Revert checked state managment using ref

[andyrichardson]

Going this route was too hacky for it's own good and can make compatibility with native problematic.

Docs need to better document this approach

const [fieldProps] = useField({
  name: "myField",
  initialValue: ['pepsi'],
});

const checkboxes = useMemo(() => [
  { label: "Coke", value: "coke" },
  { label: "Pepsi", value: "pepsi" },
], []);

return (
  <>
    {checkboxes.map(({ label, value }) => (
      <div key={value}>
        <input type="checkbox" {...fieldProps} value={value} checked={fieldProps.value.includes(value)} />
       {label}
      </div>
    )}
  </>
);