[0.3.x] Fix react-inertia setError bug

[yo-goto]

It seems that we cannot use the setError method of laravel-precognition-react-inertia in the current implementation.

Upon inspecting the internals, it appears that the setError method uses setErrors internally.
However, due to a mistake with this variable, attempting to use setError was resulting in it being interpreted as a non-existent property and couldn't be used.
I have made the necessary corrections to address this issue, so setError should now be properly usable.

[timacdonald]

This is unused.

[timacdonald]

This PR now removes all references to this.

When destructing an function in JS, if the function references "this" it's value is lost during the destructure.

const obj = {
    foo() {
        return this
    }
}

console.log(obj.foo() === obj)
// true

const { foo } = obj

console.log(foo() === obj)
// false

To allow better destructuring, I've removed all references to "this"

[yo-goto]

Yep. Thank you for improving!